2012 PGT Physics Part1

8/10/2019 2012 PGT Physics Part1

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Chief Advisor

Rashmi Krishnan, IAS

Director, SCERT

GuidanceDr. Pratibha Sharma,Joint Director, SCERT

Academic Co-ordinator and Editor

Dr.Rajesh Kumar, Principal, DIET Daryaganj

Sapna Yadav, Sr. Lecturer, SCERT

Contributors

Prof. B.K Sharma (Retd.) Professor, NCERT

Dr. R.P Sharma, Academic Consultant, CBSE

Pundrikaksh Kaundinya, Vice Principal, RPVV Kishangaj

Sher Singh, Principal, Navyug School, Lodhi Road

Davendra Kumar, Lecturer, RPVV, Yamuna Vihar

Girija Shankar, Lecturer, RPVV, Surajmal Vihar

R.Rangarajan , Lecturer, DTEA , Sr.Secondary School , Lodhi Road

Neelam Batra , Lecturer, D.C. Arya, Sr. Sec. School, Lodhi ColonyChitra Goel, Retd Vice Principal

Dr.Rajesh Kumar, Principal, DIET Daryaganj

Sapna Yadav , Sr. Lecturer , SCERT

Publication Officer

Mr. Mukesh Yadav

Publication Team

Sh. Navin Kumar, Ms. Radha, Sh. Jai Baghwan

Published by : State Council of Educational Research & Training, New Delhi and printed at

Educational Stores, S-5, Bsr. Road Ind. Area, Ghaziabad (U.P.)


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Safety Precautions for Students in Physics Laboratory

Designing of all science laboratories according to necessary norms and standards.

Two wide doors for unobstructed exits from the laboratory.

Adequate number of fire extinguishers near science laboratories.

Periodical checking of vulnerable points in the laboratories in relation to possibility of anymishappening.

Periodical checking of electrical fittings/ insulations for replacement and repairs.

Timely and repeated instructions to students for careful handling of equipments in the laboratory.

Display of do's and dont's in the laboratory at prominent places.

Safe and secure storage of all Equipments

Proper labelling and upkeep of Equipments

Careful supervision of students while doing practical work.

Advance precautionary arrangements to meet any emergency situations.

Conduct of any additional experimental work only under supervision and with due advance permission. Availability of First Aid and basic medical facilities in the school.

Proper location of the laboratories.

How to make the learning of the difficult topics easier?

Do's Und Dont's

1. Do not take the word difficult while teaching and you be positive yourself.

2. Do not place the topic on the board - After completing tell the students that this whatit is For example topics like Potentiometer

3. Try to build the topic from the basics of the basic while teaching.

4. Do not draw the diagram on board before you start the topic Do build the same as

the discussion continues.

5. Do not forget to place the arrow in circuits and Ray diagrams A mistake which can

be easily absorbed by the student.

6. Do not postpone the topic for the end of the academic session

7. Give 2-3 revision by asking question's from such identified topics at the beginning of

the class on the subsequent days.

8. Try to test these identified topics in almost all the tests if possible after prior information

to the students.

9. Do try to create interest on such topics before it is actually discussed.

10. Try to adopt an interactive approach to deal with such topics.

11. Very important a point is to think new and good approaches that may fit your students

while dealing with such topics and popularize such method.


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The Physics Student cannot afford to miss it

1. Identify the chapters in which the weight-age is more.

2. Prepare those identified chapters having more weight-age with an eye to have a sure 5 mark questionand do writing practice also with proper figures. Do the super hit questions/topics like Cyclotron,

a.c.generator, Young's experiment, Gauss's theorem, Wheatstone's bridge, potentiometer etc.., many

times before the examination, so that you do not flop during the examination because of the tilted

nature of a question.

3. Instead of leaving the topics like E.M. Waves, Principles of Communication understand to express

all definitions, interpretation of figures, Advantages and disadvantages of various devices and Applications

etc.

4. Do all the worked examples and the graphs with their Interpretation (which you can easily understand)

in a line or two from NCERT and practice them before hand.

5. Go to the examination hall with a positive frame of mind - particularly on the Physics examination

day, at least half an hour before without any books and please do not discuss any question with anyone

in this period.

6. Start the answer script with the best known question and complete all the questions that you know

without cutting and overwriting.

7. In case you are not having good Interpretation skill, first do the best known five mark questions and

try to create a good impression in the minds of the paper checker.

8. When you approach the numerical question always understand the question, recall the known concept

of the question and never try to list the formula and substitute the values.

9. Present the paper neatly and legibly without cutting and leaving space for anything that you plan to

do later, since there will not be any time to do later. If you happen to cut, do it neatly such that

the cut and the un-cut portions are distinguishable. Thinking and formatting the answer before writing

will improve you on this front.

10. Never leave any question. Write something of what you know of the answer. Remember "What you

think is wrong may be the correct answer" many a times.

Derivations

Unit-1 (Electrostatics)

Electrical / magnetic field at a point on the equatorial or axial line due to an electrical /magneticdipole

Torque experienced by a dipole placed in a uniform electric / magnetic field.

Determine the potential energy of dipole in a uniform electric field

Relation between electric field and electric potential *

Gauss's theorem and its applications


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Equivalent capacitance when capacitors are connected in parallel / series

Capacitance of parallel plate capacitor

Derive an expression for the capacity of a parallel plate capacitor with (a) dielectric slab of thickness

t < d (b) with conductor between the plates *

Using a labeled diagram, explain the principle and working of Van de Graf f generator

Unit-2 (Current Electricity) Relation between resistivity and relaxation time

Condition of balance in Wheatstone's bridge

Explain the working and principle of a potentiometer. How can it be used to (a) compare emf of

cell (b) determine internal resistance of a cell *

Unit-3 (Magnetic Effect of Current and Magnetism)

Magnetic field due to a straight conductor / coil carrying current

Force experienced by (a) charge moving in electric field (b) current carrying conductor (c) torque

on coil in magnetic field. Ampere's circuital law and its application for determining magnetic field in solenoids and toroidal.*

Force between two parallel wires carrying current *

Describe the principle, construction and working of a moving coil galvanometer with a labeled diagram. *

Explain with the help of a labeled diagram, the underlying principle, construction and working of

a cyclotron frequency and total K.E. *

Unit-4 (Electromagnetic Induction and Alternating Current)

Write five differences between dia, Para and Ferro magnetic substances.*

magnetic field at a point on the equatorial or axial line due to an electrical / magnetic dipole

Unit-5 (Electromagnetic Waves)

Determination of (a) coefficient of self induction (b) mutual induction in solenoids *

Energy stored in an (a) inductor (b) capacitor *

Distinguish between resistance, reactance and impedance.

Derive an expression for (a) current in LCR series circuit using phasor diagram and power or LCR

circuit *

Explain with the help of a labeled diagram, the principle, construction and working of a transformer.

Why is it used for power transmission? *

Explain with the help of labeled diagram, the principle, construction and working of an AC generator* Explain Hertz's experiment for producing electromagnetic waves

Unit-6 (Optics)

Deduce laws of refraction & reflection on me basis of Huygens's principle. *

Interference by Young's double slit experiment, determination of fringe width and condition for maxima

and minima.*


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Diffraction at a single slit - determination of fringe width of central max. *

Diffraction at a single slit - determination of fringe width of central max. *

Polarisation - Malu's law & Brewster's law *

Mirror formula for concave and convex mirrors

Define critical angle and write condition for total internal reflection. Obtain an expression for refractive

index in terms of critical angle

Lens formula for convex and concave lenses

Derive an expression for refraction at spherical surfaces.

Deduce lens maker's formula for a biconvex lens *

Obtain an expression for the refractive index of the material of a prism in terms of refracting angle

and angle of minimum deviation.

Structure of eye and its defects and rectification

Draw a labeled diagram and determine the magnification and resolving power of (a) simple microscope

(b) compound microscope (c) astronomical telescope and (d) reflecting type telescope *

Explain dispersion and rainbow formation

Unit-7 (Dual Nature of Mather)

State the laws of photoelectric effect. Establish Einstein's photoelectric relation *

Explain Davison Germer experiment and show how it proved De Broglie's theory of matter waves. *

Determination of wavelength associated with electron *

Unit-8 (Atom Nuclei)

Short notes on , and Y decay

State law of radioactive decay and obtain expression for N *

Bohr's Postulate. Expression for radius, K.E, P.E, Total energy, energy spectrum with energy level

diagram. *

Unit-9 (Electronic Devices)

Difference between (a) n and p type semiconductors (b) intrinsic and extrinsic semiconductors

Draw the circuit to study the characteristics of p-n junction diode in forward and reverse bias. Sketch

the V I graph for the same

Explain the use of p-n junction diode as a rectifier. Draw the circuit diagram of (a) full wave rectifier

and (b) half wave rectifier. Draw input and output waveforms for them *

Draw the circuit to study the output and input characteristics of a common emitter amplifier. Sketch

the V I graph for the same. *

With the help of a circuit diagram, explain the working of a pnp / npn transistor as an amplifier incommon emitter mode *

With the help of a circuit diagram, explain the working of a pnp / npn transistor as a switch in common

emitter mode

Discuss the working of a transistor as an oscillator. *

Realization of AND, OR and NOT gates


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Unit-10 (Communication System)

What is a communication system? Describe the constituents of a communication system

Write short notes using block diagram on (a) ground waves (b) sky waves (c) space wave obtain

expression for range for LOG transmission (d) modulation index.*

What do the following terms refer to in communication: transducer, base band, bandwidth, attenuation,

modulation, demodulation, noise, modulation index.

What is modulation? Why is modulation required?

What is demodulation? Draw a block diagram to show receiver and demodulation

Draw block diagram for modulation process and determine the bandwidth for amplitude modulation

*very important

Important diagrams

Van de Graft generator neatly labeled.

Moving coil galvanometer and cyclotron neatly labeled

Microscope simple & compound

Telescope refracting & reflecting

Ray diagram for lens maker's formula & Lens formula

A.C.generator and transformer

Photoelectric effect and bavison Germer experiment

Amplifier (npn & pnp transistor), switch and Oscillator.

Rectifier (full wave & half wave)

Circuit diagram of potentiometer (comparing emf, internal resistance) and Meter Bridge for determining

resistance.

Electrical field due to a point charge, charge on parallel plates Binding energy per nucleon mass

no. (graph)

Semi conductorLED, Photodiode, solar cell, Zener diode, diode and their characteristics

Schematic representation of (a) modulation (b) demodulation (c) wave propagation (d) global satellite

communication.


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PHYSICS (Code No. 042)

Senior Secondary stage of school education is a stage of transition from general education to discipline-

based focus on curriculum. The present updated syllabus keeps in view the rigour and depth of disciplinary

approach as well as the comprehension level of learners. Due care has also been taken that the syllabus

is comparable to the international standards. Salient features of the syllabus include:

Emphasis on basic conceptual understanding of the content.

Emphasis on use of SI units, symbols, nomenclature of physical quantities and formulations as

per international standards.

Providing logical sequencing of units of the subject matter and proper placement of concepts

with their linkage for better learning.

Reducing the curriculum load by eliminating overlapping of concepts/ content within the discipline

and other disciplines.

Promotion of process-skills, problem-solving abilities and applications of Physics concepts.Besides, the syllabus also attempts to

strengthen the concepts developed at the secondary stage to provide firm foundation for further

learning in the subject.

expose the learners to different processes used in Physics-related industrial and technological

applications.

develop process-skills and experimental, observational, manipulative, decision making and

investigatory skills in the learners.

promote problem solving abilities and creative thinking in learners.

develop conceptual competence in the learners and make them realize and appreciate the interface

of Physics with other disciplines.


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Unit vector; Resolution of a vector in a plane - rectangular components. Scalar and Vector product

of vectors. Motion in a plane. Cases of uniform velocity and uniform acceleration-projectile motion.

Uniform circular motion.

Unit III: Laws of Motion (Periods 16)

Intuitive Concept of force. Inertia, Newtons first law of motion; momentum and Newtons second

law of motion; impulse; Newtons third law of motion. Law of conservation of linear momentumand its applications.

Equilibrium of concurrent forces. Static and kinetic friction, laws of friction, rolling friction,

lubrication.

Dynamics of uniform circular motion: Centripetal force, examples of circular motion (vehicle

on level circular road, vehicle on banked road).

Unit IV: Work, Energy and Power (Periods 16)

Work done by a constant force and a variable force; kinetic energy, work-energy theorem, power.

Notion of potential energy, potential energy of a spring, conservative forces: conservation of

mechanical energy (kinetic and potential energies); non-conservative forces: motion in a verticalcircle; elastic and inelastic collisions in one and two dimensions.

Unit V: Motion of System of Particles and Rigid Body (Periods 18)

Centre of mass of a two-particle system, momentum conservation and centre of mass motion.

Centre of mass of a rigid body; centre of mass of uniform rod.

Moment of a force, torque, angular momentum, conservation of angular momentum with some

examples.

Equilibrium of rigid bodies, rigid body rotation and equations of rotational motion, comparison

of linear and rotational motions; moment of inertia, radius of gyration.

Values of moments of inertia, for simple geometrical objects (no derivation). Statement of parallel

and perpendicular axes theorems and their applications.

Unit VI: Gravitation (Periods 14)

Keplars laws of planetary motion. The universal law of gravitation.

Acceleration due to gravity and its variation with altitude and depth.

Gravitational potential energy; gravitational potential. Escape velocity. Orbital velocity of a satellite.

Geo-stationary satellites.

Unit VII: Properties of Bulk Matter (Periods 28)

Elastic behaviour, Stress-strain relationship, Hookes law, Youngs modulus, bulk modulus, shear,

modulus of rigidity, poissons ratio; elastic energy.

Pressure due to a fluid column; Pascals law and its applications (hydraulic lift and hydraulic

brakes). Effect of gravity on fluid pressure.

Viscosity, Stokes law, terminal velocity, Reynolds number, streamline and turbulent flow. Critical

velocity. Bernoullis theorem and its applications.


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Surface energy and surface tension, angle of contact, excess of pressure, application of surface

tension ideas to drops, bubbles and capillary rise.

Heat, temperature, thermal expansion; thermal expansion of solids, liquids and gases, anomalous

expansion; specific heat capacity; Cp, Cv - calorimetry; change of state - latent heat capacity.

Heat transfer-conduction, convection and radiation, Qualitative ideas of Blackbody radiation green

house effect, thermal conductivity, Newtons law of cooling, Weins displacement Law, Stefans

law.

Unit VIII: Thermodynamics (Periods 12)

Thermal equilibrium and definition of temperature (zeroth law of thermodynamics). Heat, work

and internal energy. First law of thermodynamics. Isothermal and adiabatic processes.

Second law of thermodynamics: reversible and irreversible processes. Heat engines and refrigerators.

Unit IX: Behaviour of Perfect Gas and Kinetic Theory (Periods 8)

Equation of state of a perfect gas, work done in compressing a gas.

Kinetic theory of gases - assumptions, concept of pressure. Kinetic energy and temperature; rms

speed of gas molecules; degrees of freedom, law of equipartition of energy (statement only) and

application to specific heat capacities of gases; concept of mean free path, Avogadros number.

Unit X: Oscillations and Waves (Periods 28)

Periodic motion - period, frequency, displacement as a function of time. Periodic functions. Simple

harmonic motion (S.H.M) and its equation; phase; oscillations of a springrestoring force and

force constant; energy in S.H.M. Kinetic and potential energies; simple pendulum derivation

of expression for its time period; free and forced and damped oscillations (qualitative ideas only),

resonance.

Wave motion. Transverse and longitudinal waves, speed of wave motion. Displacement relation

for a progressive wave. Principle of superposition of waves, reflection of waves, standing wavesin strings and organ pipes, fundamental mode and harmonics, Beats, Doppler effect.

Practicals

Note: Every student will perform 15 experiments (8 from Section A and 7 from Section B).The

activities mentioned are for the purpose of demonstration by the teachers only. These are not

to be evaluated during the academic year. For evaluation in examination, students would be required

to perform two experiments - One from each Section.


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SECTION A

Experiments Total Periods : 60

(Any 8 experiments out of the following to be performed by the Students)

1. To measure diameter of a small spherical/cylindrical body using Vernier Callipers.

2. To measure internal diameter and depth of a given beaker/calorimeter using Vernier Callipers

and hence find its volume.3. To measure diameter of a given wire using screw gauge.

4. To measure thickness of a given sheet using screw gauge.

5. To measure volume of an irregular lamina using screw gauge.

6. To determine radius of curvature of a given spherical surface by a spherometer.

7. To determine the mass of two different objects using a beam balance.

8. To find the weight of a given body using parallelogram law of vectors.

9. Using a simple pendulum, plot L-T and L-T2graphs. Hence find the effective length of seconds

pendulum using appropriate graph.

10. To study the relationship betwen force of limiting friction and normal reaction and to find

the co-efficient of friction between a block and a horizontal surface.

11. To find the downward force, along an inclined plane, acting on a roller due to gravitational

pull of the earth and study its relationship with the angle of inclination (O) by plotting graph

between force and sin.

Activities (For the purpose of demonstration only)

1. To make a paper scale of given least count, e.g. 0.2cm, 0.5 cm.

2. To determine mass of a given body using a metre scale by principle of moments.

3. To plot a graph for a given set of data, with proper choice of scales and error bars.4. To measure the force of limiting friction for rolling of a roller on a horizontal plane.

5. To study the variation in range of a jet of water with angle of projection.

6. To study the conservation of energy of a ball rolling down on inclined plane (using a double

inclined plane).

7. To study dissipation of energy of a simple pendulum by plotting a graph between square

of amplitude and time.


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SECTION B

Experiments

(Any 7 experiments out of the following to be performed by the students)

1. To determine Youngs modulus of elasticity of the material of a given wire.

2. To find the force constant of a helical spring by plotting a graph between load and extension.

3. To study the variation in volume with pressure for a sample of air at constant temperatureby plotting graphs between P and V, and between P and I/V.

4. To determine the surface tension of water by capillary rise method.

5. To determine the coefficient of viscosity of a given viscous liquid by measuring terminal

velocity of a given spherical body.

6. To study the relationship between the temperature of a hot body and time by plotting a cooling

curve.

7. To determine specific heat capacity of a given (i) solid (ii) liquid, by method of mixtures.

8. (i) To study the relation between frequency and length of a given wire under constant tension

using sonometer.(ii) To study the relation between the length of a given wire and tension for constant frequency

using sonometer.

9. To find the speed of sound in air at room temperature using a resonance tube by two-

resonance positions.


1. To observe change of state and plot a cooling curve for molten wax.

2. To observe and explain the effect of heating on a bi-metallic strip.

3. To note the change in level of liquid in a container on heating and interpret the observations.

4. To study the effect of detergent on surface tension of water by observing capillary rise.

5. To study the factors affecting the rate of loss of heat of a liquid.

6. To study the effect of load on depression of a suitably clamped metre scale loaded at (i)

its end (ii) in the middle.

SUGGESTED LIST OF DEMONSTRATION EXPERIMENTS

CLASS XI

1. To demonstrate that a centripetal force is necessary for moving a body with a uniform speed

along a circle, and that the magnitude of this force increases with increase in angular speed.2. To demonstrate inter-conversion of potential and kinetic energy.

3. To demonstrate conservation of linear momentum.

4. To demonstrate conservation of angular momentum.

5. To demonstrate the effect of angle of launch on range of a projectile.


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6. To demonstrate that the moment of inertia of a rod changes with the change of position of a

pair of equal weights attached to the rod.

7. To study variation of volume of a gas with its pressure at constant temperature using a doctors

syringe.

8. To demonstrate Bernoullis theorem with simple illustrations

9. To demonstrate that heat capacities of equal masses of different materials are different.

10. To demonstrate free oscillations of different vibrating systems.

11. To demonstrate resonance with a set of coupled pendulums.

12. To demonstrate longitudinal and transverse waves.

13. To demonstrate the phenomenon of beats, due to superposition, of waves produced by two sources

of sound of slightly different frequencies

14. To demonstrate resonance using an open pipe.

15. To demonstrate the direction of torque.

16. To demonstrate the law of moments.

Recommended Textbooks.1. Physics Part-I, Textbook for Class XI, Published by NCERT

2. Physics Part-II, Textbook for Class XI, Published by NCERT

Class XII (Theory)

Total Periods : 180

One Paper Time: 3 Hours 70 Marks

Unit I Electrostatics 08

Unit II Current Electricity 07Unit III Magnetic effect of current & Magnetism 08

Unit IV Electromagnetic Induction and Alternating current 08

Unit V Electromagnetic Waves 03

Unit VI Optics 14

Unit VII Dual Nature of Matter 04

Unit VIII Atoms and Nuclei 06

Unit IX Electronic Devices 07

Unit X Communication Systems 05

Total 70

Unit I: Electrostatics (Periods 25)

Electric Charges; Conservation of charge, Coulombs law-force between two point charges, forces

between multiple charges; superposition principle and continuous charge distribution.

Electric field, electric field due to a point charge, electric field lines, electric dipole, electric field

due to a dipole, torque on a dipole in uniform electric fleld.


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Electric flux, statement of Gausss theorem and its applications to find field due to infinitely

long straight wire, uniformly charged infinite plane sheet and uniformly charged thin spherical

shell (field inside and outside).

Electric potential, potential difference, electric potential due to a point charge, a dipole and system

of charges; equipotential surfaces, electrical potential energy of a system of two point charges

and of electric dipole in an electrostatic field.

Conductors and insulators, free charges and bound charges inside a conductor. Dielectrics and

electric polarisation, capacitors and capacitance, combination of capacitors in series and in parallel,

capacitance of a parallel plate capacitor with and without dielectric medium between the plates,

energy stored in a capacitor. Van de Graaff generator.

Unit II: Current Electricity (Periods 22)

Electric current, flow of electric charges in a metallic conductor, drift velocity, mobility and their

relation with electric current; Ohms law, electrical resistance, V-I characteristics (linear and non-

linear), electrical energy and power, electrical resistivity and conductivity. Carbon resistors, colour

code for carbon resistors; series and parallel combinations of resistors; temperature dependence

of resistance.

Internal resistance of a cell, potential difference and emf of a cell,combination of cells in series

and in parallel.

Kirchhoffs laws and simple applications. Wheatstone bridge, metre bridge.

Potentiometer - principle and its applications to measure potential difference and for comparing

emf of two cells; measurement of internal resistance of a cell.

Unit III: Magnetic Effects of Current and Magnetism (Periods 25)

Concept of magnetic field, Oersteds experiment.

Biot - Savart law and its application to current carrying circular loop.

Amperes law and its applications to infinitely long straight wire. Straight and toroidal solenoids,

Force on a moving charge in uniform magnetic and electric fields. Cyclotron.

Force on a current-carrying conductor in a uniform magnetic field. Force between two parallel

current-carrying conductors-definition of ampere. Torque experienced by a current loop in uniform

magnetic field; moving coil galvanometer-its current sensitivity and conversion to ammeter and

voltmeter.

Current loop as a magnetic dipole and its magnetic dipole moment. Magnetic dipole momentof a revolving electron. Magnetic field intensity due to a magnetic dipole (bar magnet) along

its axis and perpendicular to its axis. Torque on a magnetic dipole (bar magnet) in a uniform

magnetic field; bar magnet as an equivalent solenoid, magnetic field lines; Earths magnetic field

and magnetic elements. Para-, dia- and ferro - magnetic substances, with examples. Electromagnets

and factors affecting their strengths. Permanent magnets.


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Unit IV: Electromagnetic Induction and Alternating Currents (Periods 20)

Electromagnetic induction; Faradays laws, induced emf and current; Lenzs Law, Eddy currents.

Self and mutual induction.

Alternating currents, peak and rms value of alternating current/voltage; reactance and impedance;

LC oscillations (qualitative treatment only), LCR series circuit, resonance; power in AC circuits,

wattless current.

AC generator and transformer.

Unit V: Electromagnetic waves (Periods 4)

Need for displacement current, Electromagnetic waves and their characteristics (qualitative ideas

only). Transverse nature of electromagnetic waves.

Electromagnetic spectrum (radio waves, microwaves, infrared, visible, ultraviolet, X-rays, gamma

rays) including elementary facts about their uses.

Unit VI: Optics (Periods 30)

Reflection of light, spherical mirrors, mirror formula. Refraction of light, total internal reflection

and its applications, optical fibres, refraction at spherical surfaces, lenses, thin lens formula, lens-

maker s formula. Magnification, power of a lens, combination of thin lenses in contact combination

of a lens and a mirror. Refraction and dispersion of light through a prism.

Scattering of light - blue colour of sky and reddish apprearance of the sun at sunrise and sunset.

Optical instruments : Human eye, image formation and accommodation correction of eye defects

(myopia, hypermetropia) using lenses. Microscopes and astronomical telescopes (reflecting and

refracting) and their magnifying powers.Wave optics: Wave front and Huygens principle, relection and refraction of plane wave at a

plane surface using wave fronts. Proof of laws of reflection and refraction using Huygens principle.

Interference Youngs double slit experiment and expression for fringe width, coherent sources

and sustained interference of light. Diffraction due to a single slit, width of central maximum.

Resolving power of microscopes and astronomical telescopes. Polarisation, plane polarised light

Brewsters law, uses of plane polarised light and Polaroids.

Unit VII: Dual Nature of Matter and Radiation (Periods 8)

Dual nature of radiation. Photoelectric effect, Hertz and Lenards observations; Einsteins photoelectricequation-particle nature of light.

Matter waves-wave nature of particles, de Broglie relation. Davisson-Germer experiment

(experimental details should be omitted; only conclusion should be explained).


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Unit VIII: Atoms & Nuclei (Periods 18)

Alpha-particle scattering experiment; Rutherfords model of atom; Bohr model, energy levels,

hydrogen spectrum.

Composition and size of nucleus, atomic masses, isotopes, isobars; isotones. Radioactivity-alpha,

beta and gamma particles/rays and their properties; radioactive decay law. Mass-energy relation,

mass defect; binding energy per nucleon and its variation with mass number; nuclear fission,

nuclear fusion.

Unit IX: Electronic Devices (Periods 18)

Energy bands in solids (Qualitative ideas only) conductors, insulator and semiconductors;

semiconductor diode I-V characteristics in forward and reverse bias, diode as a rectifier; I-

V characteristics of LED, photodiode, solar cell, and Zener diode; Zener diode as a voltage

regulator. Junction transistor, transistor action, characteristics of a transistor, transistor as an amplifier

(common emitter configuration) and oscillator. Logic gates (OR, AND, NOT, NAND and NOR).

Transistor as a switch.

Unit X: Communication Systems (Periods 10)

Elements of a communication system (block diagram only); bandwidth of signals (speech, TV

and digital data); bandwidth of transmission medium. Propagation of electromagnetic waves in

the atmosphere, sky and space wave propagation. Need for modulation. Production and detection

of an amplitude-modulated wave.

Practicals

Every student will perform atleast 15 experiments (7 from section A and 8 from Section B) The

activities mentioned here should only be for the purpose of demonstration. One Project of threemarks is to be carried out by the students.

B. Evaluation Scheme for Practical Examination: Total Periods : 60

Two experiments one from each section 8+8 Marks

Practical record (experiments & activities) 6 Marks

Project 3 Marks

Viva on experiments & project 5 Marks


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Total 30 Marks

SECTION A

Experiments


1. To find resistance of a given wire using metre bridge and hence determine the specific resistance

of its material2. To determine resistance per cm of a given wire by plotting a graph of potential difference

versus current.

3. To verify the laws of combination (series/parallel) of resistances using a metre bridge.

4. To compare the emf of two given primary cells using potentiometer.

5. To determine the internal resistance of given primary cell using potentiometer.

6. To determine resistance of a galvanometer by half-deflection method and to find its figure

of merit.

7 . To convert the given galvanometer (of known resistance and figure of merit) into an ammeter

and voltmeter of desired range and to verify the same.8. To find the frequency of the a.c. mains with a sonometer.

Activities

1. To measure the resistance and impedance of an inductor with or without iron core.

2. To measure resistance, voltage (AC/DC), current (AC) and check continuity of a given circuit

using multimeter.

3. To assemble a household circuit comprising three bulbs, three (on/off) switches, a fuse and

a power source.

4. To assemble the components of a given electrical circuit.

5. To study the variation in potential drop with length of a wire for a steady current.

6. To draw the diagram of a given open circuit comprising at least a battery, resistor/rheostat,

key, ammeter and voltmeter. Mark the components that are not connected in proper order

and correct the circuit and also the circuit diagram.


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SECTION B

Experiments


1. To find the value of v for different values of u in case of a concave mirror and to find the

focal length.

2. To find the focal length of a convex mirror, using a convex lens.

3. To find the focal length of a convex lens by plotting graphs between u and v or between

1/u and 1/v.

4. To find the focal length of a concave lens, using a convex lens.

5. To determine angle of minimum deviation for a given prism by plotting a graph between

angle of incidence and angle of deviation.

6. To determine refractive index of a glass slab using a travelling microscope.

7. To find refractive index of a liquid by using (i) concave mirror, (ii) convex lens and plane

mirror.

8. To draw the I-V characteristic curve of a p-n junction in forward bias and reverse bias.

9. To draw the characteristic curve of a zener diode and to determine its reverse break down

voltage.

10. To study the characteristic of a common - emitter npn or pnp transistor and to find out the

values of current and voltage gains.


1. To identify a diode, an LED, a transistor, and IC, a resistor and a capacitor from mixed collection

of such items.

2. Use of multimeter to (i) identify base of transistor (ii) distinguish between npn and pnp type

transistors (iii) see the unidirectional flow of current in case of a diode and an LED (iv)

check whether a given electronic component (e.g. diode, transistor or IC) is in working order.

3. To study effect of intensity of light (by varying distance of the source) on an L.D.R.

4. To observe refraction and lateral deviation of a beam of light incident obliquely on a glass

slab.

5. To observe polarization of light using two Polaroids.

6. To observe diffraction of light due to a thin slit.

7. To study the nature and size of the image formed by (i) convex lens (ii) concave mirror,on a screen by using a candle and a screen (for different distances of the candle from the

lens/ mirror).

8. To obtain a lens combination with the specified focal length by using two lenses from the

given set of lenses.


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(xxiii)

SUGGESTED INVESTIGATORY PROJECTS

CLASS XII

1. To study various factors on which the internal resistance/emf of a cell depends.

2. To study the variations, in current flowing, in a circuit containing a LDR, because of a variation.

(a) in the power of the incandescent lamp, used to illuminate the LDR. (Keeping all the lamps

at a fixed distance).(b) in the distance of a incandescent lamp, (of fixed power), used to illuminate the LDR.

3. To find the refractive indices of (a) water (b) oil (transparent) using a plane mirror, a equiconvex

lens, (made from a glass of known refractive index) and an adjustable object needle.

4. To design an appropriate logic gate combinatin for a given truth table.

5. To investigate the relation between the ratio of (i) output and input voltage and

(ii) number of turns in the secondary coil and primary coil of a self designed transformer.

6. To investigate the dependence, of the angle of deviation, on the angle of incidence, using a hollow

prism filled, one by one, with different transparent fluids.

7. To estimate the charge induced on each one of the two identical styro foam (or pith) balls suspended

in a vertical plane by making use of Coulombs law.

8. To set up a common base transistor circuit and to study its input and output characteristic and

to calculate its current gain.

9. To study the factor, on which the self inductance, of a coil, depends, by observing the effect

of this coil, when put in series with a resistor/(bulb) in a circuit fed up by an a.c. source of

adjustable frequency.

10. To construct a switch using a transistor and to draw the graph between the input and output

voltage and mark the cut-off, saturation and active regions.

11. To study the earths magnatic field using a tangent galvanometer.

Recommended Textbooks.

1. Physics, Class XI, Part -I & II, Published by NCERT.

2. Physics, Class XII, Part -I & II, Published by NCERT.


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CHANGES IN PHYSICS SYLLABUS 2012-14

Following are some changes in the Syllabus of Physics at Senior Secondary Level offered

by CBSE for the session 2012-14.

Class XI

(1) Vector is clubbed in Unit II (Kinematics) from Unit IV and Unit V(Multiplication

of Vector)

(2) Add Activity NO 7 in Scetion A Experiments - Activities (For the purpose of

Demonstration only)

(3) Add the Suggested List of Demonstration Experiments Class XI

Class XII

(1) Add the Suggested List of Demonstration Experiments Class XII

(NOTE: Motivate the Students to do the Demostration)


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Suggestions to Students from a Teacher

Sleep

It is important to be well rested. Make sure to get a good night's sleep in the few days before the test.

If you don't sleep well the night before the test, don't worry about it! It is more important to sleep

well two and three nights before. You should still have the energy you need to perform at your best.

Diet

Don't change your diet right before the test. Now's not the time to try new foods, even if they are

healthier. You don't want to find out on test morning that yesterday's energy bar didn't go down well.

In the few weeks before the test, try to work a light, healthy breakfast into your daily routine. If

you already eat breakfast, good for you - don't change a thing.

Stress

Try to be aware of whatever anxiety you're feeling before test day. The first thing to remember is

that this is a natural phenomenon; your body is conditioned to raise the alarm whenever something

important is about to happen. However, because you are aware of what your body and mind are doing,

you can compensate for it.

Spend some time each day relaxing. Try to let go of all the pressures that build up during your average

day.

Visualize a successful test day experience. You already know what to expect on test day: when you'll

get each test section, how many questions there are, how much time you'll have, etc. You also know

where you are strong and where you are weak. Picture yourself confidently answering questions correctly,

and smoothly moving past trouble spots - you can come back to those questions later.

Find a family member or trusted friend with whom you can talk about the things that stress you outabout the test. When this person tells you that everything is going to be OK, believe it!

Writing Questions

Remember that a few spelling or grammar mistakes are tolerable, but you want to try to eliminate

as many of those as you can.

Try to vary your sentence length and word choice.

Before you begin to write, spend a few minutes brainstorming ideas and outlining the argument you

want to make. Planning will help you to write a well-organized and cohesive essay.

Practice and Review

Whatever you do, don't cram for the test! It is a bad strategy because you aren't going to remember

most of what you "learn" while cramming, and the odds are slim that the few things it will help you

to remember will happen to be on the test. Save the energy you would have used to cram for test

day.

In the few days before the test, do a review of the skills and concepts in which you are strong. Be

confident as you review everything that you know - and remember that confident feeling as you take

the test.


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1

1

Electric Charge

Charge is the property associated with matter due to which it produces and experiences electrical and

magnetic effects. The charge on a body arises from an excess or deficit of electrons.

Positive charge Negative charge

Glass Rod Silk

Fur Ebonite

Wool Plastic

Wool Rubber

Dry hair Comb

Magnitude of electronic charge is e =(1.6 1019C)

S.I. unit of charge is coulomb.

Point Charge

A finite size body may behave like a point charge if it produces an inverse square electric field. For

example an isolated charged sphere behave like a point charge at very large distance.

Methods of Charging

(i) By friction

(ii) By conduction (by contact)In this case transfer of charge takes place by contact.

(iii) By induction (without contact)In this case charges are Induced by external effect without any

physical contact.

Properties of Charge

(i) AdditivityTotal electric charge of a system = algebraic sum of all the positive and negative charges

contained in that system.

(ii) Conservationcharge can neither be created nor destroyed. It means that total charge of an isolatedsystem always remains constant.

(iii) QuantisationIt is the property due to which all free charges are integral multiple of electronic

charge.

Symbolically, q = ne

where q = total charge on a body

e = charge on an electron


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2

The cause of quantization is that only integral number of electrons can be transferred from one

body to another.

(iv) Charge of body does not depend upon its speed.

(v) Charge can not exist without mass though mass can exist without charge.

Coulombs Law

According to Coulombs law,

If two point charges q1, q

2 are separated by a distance r, the magnitude of the force (F) between

them is given by

F =1 2

2

q qk

rwhere k is constant of proportionality, its value in S.I. System is 9 109 Nm2c2.

In vector form

= k

If both charges are of same sign then force will be repulsive other wise attractive.

Permittivity

Value of k is also represented as k = 1/4owhere

ois called the permittivity of free space or vacuum.

Value of o = 8.854 1012 C2N1m2. Coulombs law is written as F =

If the medium between the two charges is other than vacuum, the formula becomes

F =1 2

2

m

1 q q.

4 rThe force between the charges is reduced.

m is called the permittivity of the medium.

Relative permittivity or dielectric constant

It is the ratio of permittivity of the medium to permittivity of free space.

r

=m

o

r = 1 for vacuum, 1 for air, 81 for water

Principle of Super Position

Force on any charge due to a number of other charges is the vector sum of all the forces on that

charge due to the other charges, taking one at a time. The individual forces are unaffected due to the

presence of other charges.

Electric Field

It is the space around a charge (source charge) in which any other charge (test charge) experience

an electric force due to source charge.

Intensity of electric field

Intensity of the electric field at a given point is defined as the electric force on unit positive charge

placed at that point.

Direction of electric field is same as the direction of electric force on unit positive charge. Its S.I.

Unit is NC1 or volt per meter.


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3

The electric force on a charge q placed in electric field E is given by

qE

Electric field intensity due to a point charge.

Electric field intensity at any point P due to a point charge q at O, where OP = r is

2

0

1 qr

4 r

Superposition principle

It is equal to the vector sum of the electric field intensities due to the individual charges at the

same point.

Electric Field Lines

These are the path of unit positive test charge placed in any given electric field and free to move.

Properties of electric field lines

(i) They are hypothetical lines.

(ii) The tangent to an electric field line gives direction of electric field at that point.(iii) The relative closeness of field lines indicates the relative strength of electric field at different

points.

(iv) All electric field lines originate from a positive charges and terminate on a negative charges.

They are open curves.

(v) The number of electric field lines of any charge is proportional to the magnitude of the charges.

(vi) No two electric field lines ever cross each other because field cannot have two directions at

the same point.

(vii) They are continuous curves.

(viii) These are always noamal to the surface of conductor.

(ix) Number of fields lines passing perpendicular to unit area is equal to the magnitude of electricfield.

Electric Field Line In Some Cases

(i) Electric field lines of isolated charges.

+q

q

Isolated (+q) charge Isolated (q) charge

(ii) Electric field lines of multiples charges

+q q

+q

+q


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4

(iii) Electric field lines of uniform electric field (having same magnitude and direction at every

point ) are represented by equidistance parallel straight lines with proper direction.

(iv) Electric field lines of non-uniform electric field.

Electric Dipole

An electric dipole is a pair of equal and opposite charges separated by a small distance.

It the two charges are (q) and (+q) and a is the displacement between them, then the vector quantity

is known as the electric dipole moment.

Dipole moment, p 2qa=

Direction of electric dipole moment is from negative charge to positive charge. SI unit of dipole

moments is coulomb-meter (C-m).

Electric Field Of a Dipole At a Point On Its Axis.

Consider an electric dipole consisting of two point charges q and +q separated by small distance 2a.

P is the point where field is to be calculated.

= Field at P due to +q

= Field at P due to q

Net field at P, using superposition principle

P 1 2E = E + E

, now since

[along A to P, (+ive)]

[along P to B, (-ive)]


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5

=

2 2

0

q q

(r a) (r a)

+

=

2 2

2 2 2

0

(r a) (r a)

(r a )

+

=

2 2 2 2

2 2 2

0

r a 2ra (r a 2ra)

(r a )

+ + +

=2 2 2

0

q 4ra

4 (r a )

= 2 2 2

0

p 2r

4 (r a )

direction is along the axis of the dipole (i.e.from A to P),

where p = 2qa

If a


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6

=

=

=

=

= 2 2 3/ 20 0

1 (q.2a) 1(where k )

4 (r a ) 4=

+

=

it is along B to A i.e. opposite to the direction of dipole moment.

In vector form

=

If a


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7

= Any one of the two forces (in magnitude) The perpendiculardistance between force vectors.

=

2a sin 2qa E sin =

=

sinp 2qa)=

=

E

(vector form)

(iv) Dipole is said to be in stable equilibriumif angle between and is zero and in unstable

equilibrium if angle between and is 180.

Electric Flux ()

Electric flux is defined as number of electric field lines passing through the area placed normal to

the field direction.

Electric flux d through an area element in an electric field is defined as

d =

=

ds

it is a scalar quantity.Its SI unit is Nm2 C1.

Gausss Law

It states that the electric flux entering or emerging from any closed surface is equal to 1/0 times the

value of charge enclosed by closed surface.

i.e. =osed enclosed0

qor E.ds =

Gausss law holds good for any closed surface of any shape or size. It does not depend upon

the location of charge inside the close surface.

Application of Gauss's Law

Steps for using gauss law-

(1) Assume observation point where electric field is to be determined.

(2) Assume a close surface(gaussian surface) which passes from point P.

(3) Calculate area of gaussian surface and qenclosed.

(4) Draw electric filed lines for given distribution.

(5) Determined angle between electric field and area vector at every point.

(6) Use gauss law.

Electric Field Due to a Line Charge

Let = linear charge densityP = Observation point

r = Normal distance of P from line charge.

From symmetry, E will be radially outward. Consider a cylindrical Gaussian surface of radius

r and length l passing through P.


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8

++++++++++++++++++++

l

S1

S2

S3

E E EP

Line charge

From Gauss Law E.ds

=

enclosed1 2 30

qE.dS E.dS E.dS+ + =

=

or E =

Direction of this E is radially outward.

Electric Field due to an infinite, non-conducting thin plane sheet of charge

Let P is the observation point.Surface charge density of uniformly charged sheet is .Consider a Gaussian cylindrical surface of length 2l and cross section area S passing through

point P as shown in figure.

By Gauss law enclosed

0

qE.ds =

1 2 3E.dS E.dS E.dS+ +

=

or =

=

Now, since dS1 and dS

3 are taken at equal distance from the charged sheet so

E1 = E

3 = E(Let)


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9

2ES =

E =

This expression shows that electric field at a point very close to a metal sheet does not depends

upon the distance.

Electric field due to a thin spherical shell of charge

Consider a spherical Gaussian surface of radius r passing through observation point P.

Gauss law

ds

=

osed

Chargedshell

S

SP

R

q

r o

r

P

E

(i) Field outside the cell

Gaussian surface S is of radius (r >>R)

2E.4 r .cos 0 =

or E =

2

0

q

r

This shows that the shell behaves like a point charge placed at its centre.

(ii) On the surface of shell-In this case gaussian surface is sphere itself .Hence

r = R

E = 20

1 q

4 R(iii) Inside the shell

Charge enclose is zero hence E = 0

Variation between E and r:

EE

max

0 r = R

E1

r2

r


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10

Electric Potential & Capacitance

Electrostatic Potential

The electric potential at a point in an electric field is the work done by an external force in bringing a unit

positive test charge from infinity to that point without any acceleration. potential is a scalar quantity.

potential V =

Unit of electric potential is volt.

1V = 1 volt = 1 NmC1 = 1JC1

Potential Due to a Point Charge

Let a small positive test charge q0 is brought from to A with a constant velocity.

Let electric field at any point P = E

PQ = an infinitesimally small path element

Electric force due to the field on q0 at P is

= q0

Force to be applied on q0 to move it from P to Q without imparting any acceleration to it

= q0

corresponding work,

dW = q0

.

Potential at A,

VA= [as ]

VA=

(i.e. electric potential is equal to line integral of electric field)

VA= 2

kqE

r

=

=

r

A

1 1 1 kqkq kq V

r r r

=

When q is positive, potential is positive and when q is negative potential is also negative. Potential

due to a point charge is spherically symmetric.


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11

(a) Potential Difference

Potential difference between points A & B will be,

VB V

A=

B

AE.dl

VB V

A=

B A

1 1

r r

(b) Conservation of Electric Field

As work done by electric field depends only upon the initial and final points of path so electric field

is conservative in nature.

(c) Variation of V and E With r

E

distance r

vE

Potential due to System of Charges

By superposition principle the potential V at a point due to the total charge configuration is the

algebric sum of the potential due to the individual charges.

V = V1 + V

2 + ...V

n

Potential due to a dipole

Let an electric dipole, consist of two equal and opposite charge separated by 2a. P is the observation

point.

+q

a

a

p

q

r r2 1X

r1

r

r2

P

Y

r2= OP

VP= Potential at P due to (+q) + Potential at P due to (q)

VP=

1 2

1 1kq

r r

2 1p

1 2

kq(r r )V

r r

If r >> a, then

i.e. r2 r

1=

os 2a cos

and

r1 r

2 = r, say i.e. r

1r

2 r2


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12

VP=

VP=

If , then cos = 0 i.e. potential at any point on the right bisector of the dipole is zero.(Equatorial axis)

If = 0, i.e. at a point on the axis of the dipole, (axial axis) VPbecomes maximum and is

= 2kp

r

Equipotential Surfaces

The surface at which the value of potential at every point is same is called equipotential surface.

Properties of equipotential surface

(1) No work is required to be done in moving a charge from one point to another on an equipotential

surface.

(2) No two equipotential surface intersect each other.

(3) For any charge configuration, equipotential surface through a point is normal to the electric field

at that point.

Some equipotential surfaces:

(i) For single point charge equipotential surfaces are concentric spheres.

(ii) Equipotential surfaces in a uniform electric field are planes normal to field.

E

(iii) Equipotential surface between two point charges + q and q is as follows:

+q q+q q+q q

Relation Between Field and Potential

As we know V = E.dr

hence E =

dV dr is called potential gradient

Negative sign indicates that the direction of the electric field is opposite to the direction in which

potential is increasing.


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Electric Potential Energy

Potential energy of a point charge at a point is defined as the amount of work done in bringing the

charge from an infinite distance to thet point . S.I. unit of potential energy is joule (J).Other unit

of P.E. is eV(electron volt)

Electric potential energy of a point charge in an external electric field

Potential energy U of a single charge q at a point P at distance r in an external electric fieldU = q(potential at P)=qV

p

Work done by or on a charge q in moving it from (V1) to V

2will be equal to the P.E. lost or gained

by the charge.

Thus U = q(V2 V

1)

Electric potential energy of two point charges(No external field)

Here q1and q

2are to be placed at P

1and P

2. When q

1 is brought from to P

1, no work is needed

to be done

PE of q1 = 0

q2P2r12

from

When q2is brought from to P

2, the fied of q

1already exists at P

2, against which work has to be

done.

If q2 is unit charge, this work would be = potential at P

2.

P.E. of q2 = q

2 V

P2(potential of q

1)

=

1

12

kq

r

= 1 2

12

kq q

r

U =

1 2

12

kq q

r

U =1 2

12

kq q

r

Potential energy of a system of two charge in an external field

Let point P1and P

2are in external electric field and their potentias are V

1and V

2respectively. Potential

energy of a system of two charges q1 and q

2 located at r

1 and r

2 respectively

=

1 22 2

0 12

q qq V

4 r+ +

where r12

is the distance between q1 and q

2.


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14

P.E. of an dipole in an external field

Work done in rotating the dipole through a small angle

dw =

= pE sin dwork done in rotating the dipole from 1 to 2 is given by

= =

or w = [ ]2 1pE cos cos

This work is stored as the potential energy of the system. Hence

U =

Electrostatics of Conductors

(i) Electrostatic field inside a conductor is zero.

(ii) At the surface of a charged conductor, electrostatic field must be normal to the surface at every

point.

(iii) Inside the conductor charge is zero. Charge reside only at the surface of cinductor.(iv) Electrostatic potential is constant throughout the volume of the conductor and has the same

value as on its surface.

(v) Electric field at the surface of a charged conductor

=

where is the surface charge density and is a unit vector normal to the surface.

(iv) The surface charge density () is high where the radius of curvature of the surface of theconductor is small.

(vii) Electrostatic shielding: It is the process in which any object or region is protected from electric

field. It is done by enclosing that object or region by conducting surface.

Dielectric and Polarisation

Dielectrics are non conducting substances which transmit electric effect without any actual conduction

of electricity.

e.g., vacuum, paper (waxed or oiled), mica, glass, plastic foil, fused ceramic, or air etc.

There are two type of dielectric medium.

(i) Polar dielectric:In this dielectric center of positive charge and centre of negative charge does

not coincide with each other e.g. water, HCl etc. (liquids).

(ii) Non polar dielectric:In this dielectric center of positive charge and centre of negative charge

coincide with each other. e.g. gases.Dielectric polarisation

When a dielectric is placed in a uniform electric field then the centres of positive and negative

charges in the molecule are separated, and dielectric is said to be polarised.

The polarized dielectric is equivalent to two charged surfaces with induced surface charge densities,

say + pand

p. The field produced by these surface charges opposes the external field. The total

field in the dielectric is, thereby, reduced from the case when no dielectric is present.


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15

Dielectric strength

The maximum value of the electric field at which the dielectric withstand without break down, is

called the dielectric strength of the material.

Electrostatic Capacitance

Capacitance is the capacity to store electric charges by any conductor and such conductor are

known as capacitor.If we give some charge Q to an isolated conductor, its potential increases to V.

then Q Vor, Q = CV

where C is the constant of proportionality called capacitance.

S.I. unit of capacitance is farad, F.(1 farad = 1 coulomb/volt).A conductor is said to have a capacity

of 1farad when a charge of 1 coulomb increases its potential by 1 volt.

Capacitance of an isolated conducting sphere

If a conducting sphere of radius r is given a charge Q, then the potential on the surface of the sphere is

V =

0r

=

04 r

since Q/V = C

C =

0rEstimation of one farad

If we use C = 1 farad in above relation then r = 9 109m hence farad is a very large unit.

Farad being a very large unit, other practical units are

1 microfarad = 1F = 106 farad

1 milifarad = 1mF = 103 farad

1 picofarad = 1pF = 1012 farad

Parallel plate Capacitor

In this capacitor one or more pairs of plates of conductors are seperated by a dielectric medium.

Principle

The principle of parallel plate capacitor is based on the fact that potential of a insulated conductor

is decreased when an uncharged earthed conductor is kept close to it.In this case charge of insulated

conductor remains same and more charges can be added to it.This is the way to increase the

capacitance of an insulated conductor.Capacitance of a parallel plate capacitor

Let = surface charge density = Q/AQ = Total charge on one face of either plate

A = area of one face of either plate

E = electric field between the plates

0 = permittivity of vacuum


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d = seperation between the plates

V = potential difference between the two plates

now, V = Ed

V =

V =0 0

Q d QasA

=

Q = 0AV

d

as C = Q/V hence

C =

Thus capacitance of a parallel plate capacitor depends entirely on its geometrical dimensions and

the dielectric used.

Capacitance With Dielectric Between PlatesIf K is the dielectric constant of medium between the plates of capacitor.

C =

Capacitance of a Parallel Plate Capacitor With a Conducting Slab

Let t = thickness of metal slab

As V = E (d t) +0(t)

since E = 0 inside the slab.

=

= ( )0

Q Qd t

A A

=

or,Q

V=

C =

Capacitance of a Parallel Plate capacitor with a dielectric slab

= outside field

= net field inside the dielectric slab

t = thickness of dielectric slab

r = relative permittivity of the dielectric

Now, V = E0(d t) + E

mt

+

+Q

Q

d

+

+

+

+

+

+

+

t Em

E0

Dielectricslab


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17

= 0 00 mr r

E EE (d t) t E

+ =

= 0r

1E d t 1

V =

r

1d t 1

i.e. C =

0

r

A QC

V11

=

This analysis shows that on introducing conducting or dielectric slab between the plates ofcapacitors,its capacitance increases.

Combinations of Capacitors

(i) Series combination(ii) Parallel combination

Equivalent capacity in series

In series combination,

(i) Charge stored on each capacitor is same. (ii)Potential difference across each capacitor is proportional

to its capacitance.

as V = V1 + V

2+ V

3+ ...

=1 2 3

Q Q Q...

C C C+ + +

=

1 2 3

1 1 1...

C C C+ + +

...(i)

From (i) & (ii)

=

2 3

1 1...

C C+ + +

...(ii)

Equivalent capacity in parallel

In a parallel combination,

(i) Potential difference across each capacitor is same.

(ii) Charge stored in each capacitor is proportional to its capacitance.as Q = Q

1 + Q

2 + Q

3+...

Let C = capacity of the combination

Q = CV

or CV = C1V + C

2V + C

3V + ...

or C =

2 3C C ...+ +Q Q Q

v1 1 c v2 2 c v3 3

V

+Q1

+Q2

+Q3

Q1

Q2

Q3

V

V

V+


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Energy Stored in a Capacitor

Work done in charging a capacitor is stored in form of potential energy of capacitor.This energy

is stored in the electric field between the plates.

If small charge dQ is given to a capacitor of potential V. The work required to be done for doing

it is given by

dW = V. dQ

U =

=

The energy (U) stored in the capacitor can be written in any one of the following forms:

U =

221 Q 1 1CV QV

2 C 2 2= =

Total energy stored in series or parallel combination of capacitors is equal to sum of the energiesstored in individual capacitors.

Energy density (u)

u =

21 CVTotal energy (U) 2

Volume of capacitor Ad=

= ( )20A1 1Ed

2 d Ad

u =2

0

1E

2

Common PotentialWhen two charged capacitors are connected by conducting wire then charge flow from higher to

lower potential. This flow continues till their potentials become equals and this is called common

potential.

Common Potential =

In this process of charge flows and energy loss takes place in form of heat produced in connecting

wire.

VAN-DE Graph Generator

It is a device used to accelerate charge partical. It is used in high energy nuclear physics experiments.

Principle:It is based upon the principle of electrostatic induction and corona discharge. (action of

sharp point).

Corona discharge:When a conductor carries a charge then leakage of charge takes place from its

pointed ends.

The process of spraying charge is called corona discharge (Action of sharp point).


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Construction:Motor drives the pulley P1and P

1drives pulley P

2 through an insulating belt. P

2 is

inside an air evacuated spherical metallic shell.

There are two metallic brushes placed near the insulating belt. The lower brush is connected to high

voltage battery.

The upper brush is connected with the inner surface of the spherical shell.

Working: The lower metal brush is kept at a positive potential (104volt). Due to discharging action

of sharp points, it sprays positive charge on the belt.

+++++++++++++

++++++++

+++++++++

+

+ + + ++

+

++++++++++++++

Metal brushPulley, P2

Metal

brush

Insulating belt

Ion source

Insulating column

Motor driven

pulley, P1

As the belt moves, and reaches the sphere, a negative charge is induced on the sharp ends of the

upper collecting metal brush and an equal positive charge is induced on the farther end of that

brush. This positive charge shifts immediately to the outer surface of the shell.

Due to action of sharp points of the upper metal brush, a negatively charges are sprayed on the belt.

This neutralizes the positive charge on the belt. This is repeated again and again.

Thus the positive charge on the metallic shell goes on accumulating.

Hence the potential of the spherical shell goes on increasing up to 6-8 million volts.

Answer Yourself

Very Short Questions

Q1. Draw schematically an equipotential surface of a uniform electrostatic field along x axis.

Q2. Sketch field lines due to (i) Two equal positive charges near each other (ii) dipole.

Q3. Name the physical quantity whose SI unit is volt/meter. Is it a scalar or vector quantity?

Q4. Two point charges repel each other with a force F when placed in water of dielectric constant

81. What will the force between them when placed the same distance apart in air?

Q5. Net capacitance of three identical capacitors connected in parallel is 12 microfarad. What will

be the net capacitance when two are connected in (i) parallel (ii)series.

Q6. A charge q is placed at the centre of an imaginary spherical surface. What will be the electric

flux due to this charge through any half of the sphere?


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Q7. Sketch the electric field vs distance( from the centre) graph for (i) a long charged rod with linear

charge density < 0 (ii) spherical shell of radius R and charge Q > 0.

Q8. Diagrammatically represent the position of a dipole in (i) stable (ii) unstable equilibrium when

placed in a uniform electric field.

Q9. A charge Q is distributed over a metal sphere of radius R.What is the electric field and electric

potential at the centre?

Q10. The relative permittivity of mica is 6. What is its absolute permittivity?Q11. If q

1q

2 > 0, and if q

1q

2< 0 what can we say about the nature of force?

Q12. Although ordinary rubber is an insulator, the tyres (rubber) of aircraft are made slightly conducting.

Why?

Q13. The force between two charges separated by distance r in air is 10N. When the charges are placed

same distance apart in a medium of dielectric constant K, the force between them is 2N. What

is the value of K?

Q14. A square ABCD has each side 1 m. Four charges + 0.02 C, + 0.04 C, + 0.06 C and + 0.02 C

are placed at A, B, C and D respectively. Find the potential at the centre of the square.

Short Questions

Q1. Find the number of field lines originating from a point charge of q = 8.854 C.

Q2. What is the work done in rotating a dipole from its unstable equilibrium to stable equilibrium?

Does the energy of the dipole increase or decrease?

Q3. Derive an expression for the work done in rotating an electric dipole from its equilibrium position

to an angle with the uniform electric field.

Q4. The figure shows the Q (charge) versus V (potential) graph for a combination of two capacitors.

Identify the graph representing the parallel combination.

Q5. Calculate the work done in taking a charge of 1C in a uniform electric field of 10 N/C from

BtoC given AB= 5cm along the field and AC= 10cm perpendicular to electric field.

Q6. Draw equipotential surface for a (i) point charge (ii) dipole with same nature of charge.

Q7. What is the ratio of electric field intensity at a point on the equatorial line to the field on axial

line when the point is at the same distance from the centre of the dipole?


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Q8. Show that the electric field intensity can be given as negative of potential gradient.

Q9. For an isolated parallel plate capacitor of capacitance C and potential V, what will happen to

(i) charge on the plates (ii) potential difference across the plates (iii) field between the plates

(iv) energy stored in the capacitor, when the distance between the plates is increased?

Q10. Obtain an expression for the field due to electric dipole at any point on the equatorial line.

Q11. Can two equi potential surfaces intersect each other? Give reasons.

Two charges q and +q are located at pointsA(0,0,-a) and B (0,0,+a) respectively. How muchwork is done in moving a test charge from point P(7,0,0) to Q (-3,0,0)? (zero)

Q12. Define electrostatic potential and its unit. Obtain expression for electrostatic potential at a point

P in the field due to a point charge.

Q13. What is polarization of charge? With the help of a diagram show why the electric field between

the plates of capacitor reduces on introducing a dielectric slab. Define dielectric constant on the

basis of these fields.

Q14. Using Gausss theorem in electrostatics, deduce an expression for electric field intensity due to

a charged electric shell at a point in (i) inside (ii) on its surface (iii)outside it. Graphically show

the variation of electric field intensity with distance from the centre of shell.

Q15. Three capacitors are connected first in series and then in parallel. Find the equivalent capacitancefor each type of combination.

Q16. Derive an expression for the energy density of a parallel plate capacitor.

Q17. What should be the position of charge q=5 C for it to be in equilibrium on the line joining

two charges q1= - 4 C and q

2= 10C separated by 9cm. Will the position change for any other

value of charge q. (9cm from- 4 C)

Q18. Two point charges 4e and e each, at a separation r in air, exert force of magnitude F. They are

immersed in a medium of dielectric constant 16. What should be the separation between the charges

so that the force between them remains unchanged (1/4 the original separation)

Long Questions

Q1. State the principle of Van De Graff generator. Explain its working with the help of a neat labeled

diagram.

Q2. Derive an expression for the strength of electric field intensity at a point on the axis of a uniformly

charged circular coil of radius R carrying charge Q.

Q3. Derive an expression for potential at any point distant r from the centre O of dipole making

an angle with the dipole.

Q4. Suppose that three points are set at equal distance r = 90cm from the centre of a dipole, point

Aand B are on either side of the dipole on the axis (A closer to +ve charge and B closer to

B) point C which is on the perpendicular bisector through the line joining the charges. What

would be the electric potential due to the dipole of dipole t 3.610-19

Cm at points A,B and C.Q5. Derive an expression for capacitance of parallel plate capacitor with dielectric slab of thickness

t (t < d) between the plates separated by distance d. How would the following (i) energy (ii)

charge, (iii) potential be affected if dielectric slab is introduced with battery disconnected, (b)

dielectric slab is introduced after the battery is disconnected.

Q6. Derive an expression for torque experienced by dipole placed in uniform electric field. Hence

define electric dipole moment.


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Q7. State Gausss theorem. Derive an expression for the electric field due to a charged plane sheet.

Find the potential difference between the plates of a parallel plate capacitor having surface density

of charge 5x10-8C/m2 with the separation between plates being 4mm.

Q1. A point charge Q is placed at point O as shown in fig. Is the potential difference Va Vb positive,negative or zero, if Q is (i) positive (ii) negative charge.

O A B

Q2. Electric dipole moment of Cu S04molecule is 3.2x10-32Cm. Find the separation between copper

and sulphate ions.

Q3. The electric potential V at any point in space is given V=20x3volt, where x is in meter. Calculate

the electric intensity at point P (1,0,2).

Q4. What is electric field between the plates with separation of 2cm, (i) with air (ii) dielectric medium

of dielectric constant K, electric potential of each plate as marked in fig

Q5. Two point charges 6 C and 2 C are separated by 3cm in free space. Calculate the work done

in separating them to infinity. (3.6joule)

Q6. BC is an equilateral triangle of side10cm. D is the mid point of BC, charge 100 C, -100 C

and 75 C are placed at B, C, and D respectively. What is the force experienced by a 1 C

positive charge placed at A. (92103N)Q7. In the following fig. calculate the potential difference across capacitor C2 Given potential at A

is 90 V. C1=20 F., C2=30 F. and C3= 15 F.

(20V)

Q8. A point charge develops an electric field of 40 N/C and a potential difference of 10J/C at a point.

Calculate the magnitude of the charge and the distance from the point charge. (2.9x10-10C, 25cm)

Q9. For what value of C does the equivalent capacitance between A and B is 1. Find the given circuit

(2microfarad)

To be Learnt


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Q10. What should be the charge on a sphere of radius 4cm, so that when it is brought in contact

with another sphere of radius 2cm carrying charge of 10 C, there is no net transfer of charge?

Q11. Two capacitors of capacitances C1 and C2 are charged to potentials V1 and V2 respectively.

The capacitors are joined through a conducting wire. What is the value of common potential?

1. Direction of electric field is along decreasing potential.

2. Formulae of dipole moment

3. E = -dV/dr

4. Same as 3

5. Refer NCERT example of potential

6. Use coulombs law and principle of vector addition.

7. Charge remains same in all capacitors in series combination. Q = CV

8. E/V = 1/r

9. Apply capacitor combination principle

10. No charge transfer if potential is same

11. Potential = net charge /net capacitor

Pedagogical Remark


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2

The flow of charge is known as current electricity. The rate of flow of charge is called electric

current.

I =q

t

q = ne where n is an integer

and e = 1.6 1019C.

The SI unit of electric current is ampere (A).

In metals or conductors free electrons move randomely in all possible directions and collide with

atoms of the matter. They move in straight line between two successive collisions. When electric

field is applied across a conductor the electrons get accelerated which may not be in the direction

of velocity of electron in absence of electric field. Hence the electrons do not follow straight line

path in presence of electric field.

(a) (b)

Fig. 2.1

The average velocity of all free electrons in a conductor in presence

of electric field is called drift velocity. The velocity of free electron

just after the collision becomes zero and just before the collision

remains maximum i.e., v = a where is the time between two

sucessive collision and called relaxation time.Fig. 2.2

Let n be the number of free electrons per unit volume in a conductor of length l and area ofcorss-section A, then the total charge of free electrons,

q = neAl

And on applying potential difference V across it, the electric current,

I =


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or I = neAvd

where vd = drift velocity

If u1, u

2...u

n be the initial and v

1, v

2 ... v

n that the final velocities of free electrons than

v =

2 1 2... ...n nu u v v v

n

+ + + +

=

ne En

m

n

=eE

m

=

.

decreases with increases in temperature, hence drift velocity decreases with increase in temperature.

I = neAvd

=

eV

ml

=

AV

l

or =

l

A

V

I = R (resistance)

R =

l

A

Also R =l

A

Where =

called resistivity or specific resistance. It depends

upon the material and temperature.

Ohm's law states that the ratio of potential difference and current flowing though a conductoris constant if all external condition like temperature, etc., are remain unchanged.

= R

The conductors who obey the Ohm's law are called Ohmic and those do not Obey are called non-

ohmic conductor.


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The I V graph of ohmic conductor is straight line. Fig. 2.3

Fig. 2.3

When resistances are connected in series the equivalent resistance,

Fig. 2.4

R = R1 + R

2 + R

3

In series the equivalent resistance is greater than the largest resistance present in the combination.The current in all resistances remains same and potential difference distributes in direct ratio of

their resistances.

I1 = I

2

and =

Fig. 2.5

When resistances are connected across two same points, the combination is called parallel combination.

Fig. 2.6.

In paralle combination the equivalent resistance, R in given by

=

in parallel combination the equivalent resistance is less than the smallest resistance present in the

combination.

Fig. 2.6


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The p.d. aross each resistor is same and current distibutes in

inverse ratio of the resistances

V1 = V

2

and1

2

I

I =

When temperature of Ohmic conductor increases, the mean free path and relaxation time decreases.

Therefore, the resistivity =

increases.

The change in resistivity is directly proportional to the original resistivity and change in temperature

()

0

or = 0

where is called the temperature co-efficient of resistivity. is positive for metals and negative

for semiconducture. The new resistivity,

= 0 +

= 0 +

0

= 0 (1 + )

correspondingly R = R0 (1 + )

The carbon resistors are coded by coloured rings. For resistances three coloured rings are used.

The coloures are coded as

Fig. 2.8

Black Brown Red Orange Yellow Green Blue Violet Gray White

Bl Br R O Y G G W

0 1 2 3 4 5 6 7 8 9

Table 2.1

The code of first second and third coloured bands give thefirst digit, second digit and number of zeroes followed by

second digit of the resistance value.

Electric cell is the simplest source of electrical energy. The

cell consists of electrolyte and electrodes.

The resistance offered by cell (electrolyte and electrods) is

called internal resistance of the cell (r). Fig. 2.9

Fig. 2.7


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The internal resistance depends upon the nature of material

of electrodes and electrolyte.

Concentration of electrolyte. It increases with increase in

concentration.

Surface area of electrodes. It decreases with increase in surface area of electrodes.

Seperation of the electrodes. It increase with increase in seperation of electrodes. Temperature. It decrease with increase in temperature.

The amount of worce done in circulating a unit positive charge in a closed circuit including the cell

is called electro motive force (emf).

Current drawn from the cell

I =

I =

where R = external resistance and r is internal resistance

IR + Ir =

V = IR

= V + Ir

If I = 0, = V

emf can also be defined as the terminal voltage of the cell when no current is drawn from the

cell.

If n identical cells each of emf and internal resistance r are connected in series with external

resistance R, the current I can be given by

I =

If r


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When the cell is short-circuited, the external resistance becomes zero.

I =

E

r) r=

+

i.e., short-circuit current of a cell is maximum while terminal voltage is zero.

Power transfer to the load by the cell will be

P = I2R =

2

2

R

(R r)+

If R = 0 or the P will be minimum.

For maximum value of P

dP

dR= 0 i.e.,

2

2

2012 PGT Physics Part1

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Transcript of 2012 PGT Physics Part1