Important question of electricity Class 12Q.1 Define drift velocity and derive an expression for it and prove that I = neAVd

Q.2 State Kirchhoff’s laws and apply it to derive Wheatstone’s bridge principle.Q.3 Draw V - I graph for ohmic and non-ohmic materials. Give one example for each.Q.4 Define the term 'resistivity' and write its S. I. Unit. Derive the expression for theresistivity of a conductor in terms of number density of free electrons and relaxation time.Q.5 State the principle of potentiometer. Draw a circuit diagram used to compare the e.m.f. of two primary cells. Write the formula used. How can the sensitivity of a potentiometer be increased?Q.6 Two cells of emf 1.5 V and 2 V and internal resistance 1 ohm and 2 ohm respectively are connected in parallel to pass a current in the same direction through an external resistance of 5 ohm. (i) Draw the circuit diagram. (ii) Using Kirchhoff's laws, calculate the current through each branch of the circuit and potential difference across the 5 ohm resistor.Q.7 A cylindrical metallic wire is stretched to increase its length by 5%. Calculate the percentage change in its resistance.Q.8.Q.9 (a) Define emf. of a cell? On what factors does it depend?(b) Figure below shows a 2.0v potentiometer used for the determination of internal resistance of a 1.5v cell. The balance point of the cell in open circuit is 76.3cm. When a resistance of 9.5is used in external circuit of the cell the balance point shifts to 64.8cm length of the potentiometer. Determine the internal resistance of the cell

. Q.10

Physics Classes By Er.Shyam Pachori add: C.L 81 D.D Nagar Mob.: 9039803981 Batches MWF Time: 3:30 - 5 pm

Class 12 important questions of EMI "OM Sai Ram"

Q.1. The magnitude of electric current is increasing from A towards B. If there is any induced current in the loop as shown in the fig what will be its direction?Q.2 Which physical quantity is called the INERTIA OF ELECTRICITY? Why is its called so?Q.3 Define 1 Henry.Q.4 Two bar magnets are quickly moved towards a metallic loop connected across acapacitor 'C' as shown in the figure. Predict the polarity of the capacitor.

Q.5 Name and state the law, which gives the direction of induced e.m.f. inelectromagnetic induction.Q.6 What are eddy currents ? Write any two applications of eddy currents.Q.7 What is the basic requirement to induce the electric current in a coil ?Q.8 A current is induced in coil C1 due to the motion of current carrying coil C2.(a) Write any two ways by which a large deflection can be obtained in thegalvanometer G. (b) Suggest an alternative device to demonstrate the induced currentin place of a galvanometer.

Q.9. In the figure given below, a bar magnet moving towards the right or left induces an e.m.f. in the coils (1) and (2). Find giving reason, the directions of the direction of the induced currents through the resistors AB and CD when the magnet is moving (a) towards the right, and (b) towards the left.

Q.10 The magnetic flux linked with a coil varies with time as Ф = 3t2 + 4t + 9 weber. What is the induced emf at t = 2 ? Q.11 A circular coil of radius 8 cm and 20 turns rotates about its vertical diameter with anangular speed of 50 s-1 in a uniform horizontal magnetic field of magnitude 3 x 10-2 T. Find themaximum and average value of the emf induced in the coil.Q.12 Define self-inductance and give its S. I . unit. Derive an expression for self- inductance ofa long, air-cored solenoid of length l, radius r, and having N number of turns.Q.13 A train is moving in the North-South direction with a speed of 72 km/hr. Find the amount of emf generated between two wheels, if the length of axle be 2m. Assume that the vertical component of earth’s field is 8x10-5wbm-2.Q.14 What is the basic principle of Lenz’s Law, explain how it follow law of conservation of energy.Q.15 What do you understand by Inductance and derive the expression for energy stored in an inductor.Q.16 An a.c. generator consist of a coil of 50 turns, area 2.5m2 rotating at an angular speed of 60 rad/s in uniform magnetic field of B = 0.3 T between two fixed pole pieces. Given R = 500 Ώ(i) Find the maximum current drawn from the generator?(ii) What will be the orientation of the coil wrt. B to have max and zero magnetic flux? Q.17 Monica’s mother was heating food on a gas stove. Her friend Deepti came and saw her mother heating food on the gas stove. Deepti told Monica’s mother, “Why don’t you buy a microwave oven”? Monica’s mother replied at once that she doesn’t like to use microwave oven. Monica and Deepti made it clear that microwave is not harmful for cooking food. This is an easy and safe process. Monica’s mother got convinced and ordered for a microwave oven. Monica’s mother then arranged

a small party for her friends and told them the advantages of a microwave oven.• What value was displayed by Monica and her friend?• What value was displayed by Monica’s mother?• What value was displayed by Monica to her friends? ( Value based Question )Q.18 Derive expression of mutual inductance of two long coaxial solenoid.Q.19 What is motional emf. Deduce an expression for it. State Fleming's right hand rule to find the direction of induced emf.Q.20 Describe briefly, with the help of a labelled diagram, the basic elements of an A.C.generator. State its underlying principle. Show diagrammatically how an alternatingemf is generated by a loop of wire rotating in a magnetic field. Write the expressionfor the instantaneous value of the emf induced in the rotating loop.

important questions of magnetic effect and magnetism class 12Q.1. Where on the surface of Earth is the angle of dip 90 ?Q.2 Which material is used for making permanent magnet & why?Q.3 An electron beam projected along +X-axis, experiences a force due to a magnetic field along the +Y-axis. What is the direction of the magnetic field?Q.4 Why should the spring/suspension wire in a moving coil galvanometer have low torsional constant?Q.5 Why a galvanometer cannot be used as an ammeter directly?Q.6. How is the magnetic field inside a given solenoid made strong ?Q.7 Write the expression for Lorentz magnetic force on a particle of charge 'q' moving with velocity V in a magnetic field B .Show that no work is done by this force on the charged particle.

Q.8 Draw magnetic field lines when a (i) diamagnetic, (ii) paramagnetic substance is placed in an external magnetic field. Which magnetic property distinguishes this behaviour of the field lines due to the two substances ?Q.9 Derive an expression for magnetic field on the axial line of circular loop of radius ‘a’ and carrying current I at a distance x from the centre.Q.10 Write the relation for the force F acting on a charge carrier q moving with a Velocity V through a magnetic field B in vector notation. Using this relation, deduce the conditions under which this force will be (i) maximum (ii) minimum. Q.11 Compare hysteresis curve of soft iron and steel , which dissipate more energy and why ?Q.12 Define the terms 'Magnetic Dip' and 'Magnetic Declination' with the help of relevant diagrams.Q.13. What is radial magnetic field? What is its importance in a moving coil galvanometer? How is a radial magnetic field realized in moving coil galvanometers?Q.14 An electron and a proton moving parallel to each other in the same direction with equal momenta enter into a uniform magnetic field which is at right angle to their velocities. Calculate the ratio of radii of the circular path.Q.15. State and prove Ampere’s circuital theorem and apply it to find the magnetic field inside a solenoid .Q.16 Obtain an expression for the magnetic moment of an electron moving with a speed ‘v’ in a circular orbit of radius ‘r’. How does this magnetic moment change when :(i) the frequency of revolution is doubled?(ii) the orbital radius is halved?Q.17 Pooja went to the market with her mother and decided to come back home by metro. At Metro station they were made to pass through a gate way for security check. Pooja passed through it and was waiting for her mother to come. She heard a long beep when her mother passed through metal detector. Pooja was confused why metal detector beeped in case of her mother. She asked the duty staff, who explained her in detail. Both were satisfied with the security system.• What values are displayed by pooja• What is cause of sound through metal detector• Write the Principle on which a Metal detector works ( Value based Question )Q.18 Describe the principle and working of a cyclotron. Explain why an electron cannot be accelerated using a cyclotron , prove that time period does not depend upon speed of the particle.Q.19 A galvanometer with a coil of resistance 120 ohm shows full scale deflection for a current of 2.5 MA. How will you convert the galvanometer into an ammeter of range 0 to 7.5 A? Determine the net resistance of the ammeter.

When an ammeter is put in a circuit, does it read slightly less or more than the actual current in the original circuit? Justify your answer. Q.20 Derive an expression for the force between long straight conductors carrying current and hence define 1 ampere , what happen when direction of current reversed in one conductor.

Worksheet Of ElectrostaticQ1. If 109 electrons move out of a body to another body every second, how much time is required to get a total charge of 1 C on the other body?Q2. How much positive and negative charge is there in a cup of water?Q3. A polythene piece rubbed with wool is found to have a negative charge of 3 × 10–7 C.(a) Estimate the number of electrons transferred (from which to which?) (b) Is there a transfer of mass from wool to polythene?Q4. A point charge of 2.0 μC is at the centre of a cubic Gaussian surface 9.0 cm on edge. What is the net electric flux through the surface?Q5. An oil drop of 12 excess electrons is held stationary under a constant electric field of 2.55 × 104 NC–1 in Millikan’s oil drop experiment. The density of the oil is 1.26 g cm–

3. Estimate the radius of the drop. (g = 9.81 m s–2; e = 1.60 × 10–19 C).Q.6 A uniformly charged conducting sphere of 2.4 m diameter has a surface charge density of 80.0 μC/m2. (a) Find the charge on the sphere. (b) What is the total electric flux leaving the surface of the sphere?Q.7A system has two charges qA = 2.5 × 10–7 C and qB = –2.5 × 10–7 C located at points A: (0, 0, –15 cm) and B: (0,0, +15 cm), respectively. What are the total charge and electric dipole moment of the system?Q.8Four point charges qA = 2 μC, qB = –5 μC, qC = 2 μC, and qD = –5 μC are located at the corners of a square ABCD of side 10 cm. What is the force on a charge of 1 μC placed at the centre of the square?Q.9(a) An electrostatic field line is a continuous curve. That is, a field line cannot have sudden breaks. Why not? (b) Explain why two field lines never cross each other at any point? Q.10 Two point charges qA = 3µC and qB = –3 µC are located 20 cm apart in vacuum.(a) What is the electric field at the midpoint O of the line AB joining the two charges?(b) If a negative test charge of magnitude 1.5 × 10–9 C is placed at this point, what is the force experienced by the test charge?Q.11. (a) Calculate the potential at a point P due to a charge of 4 × 10–7C located 9 cm away.(b) Hence obtain the work done in bringing a charge of 2 × 10–9 C from infinity to the point P. Does the answer depend on the path along which the charge is brought?

Q.12 Two charges 3 × 10–8 C and –2 × 10–8 C are located 15 cm apart. At what point on

the line joining the two charges is the electric potential zero? Take the potential at

infinity to be zero.Q13. A slab of material of dielectric constant K has the same area as the plates of a parallel-plate capacitor but has a thickness (3/4)d, where d is the separation of the plates. How is the capacitance changed when the slab is inserted between the plates?

Q.14 A parallel plate capacitor with air between the plates has acapacitance of 8 pF .What will be the capacitance if the distance between the plates is reduced by half, and the space between them is filled with a substance of dielectric constant 6?Q.15 Three capacitors of capacitances 2 pF, 3 pF and 4 pF are connected in parallel.(a) What is the total capacitance of the combination?(b) Determine the charge on each capacitor if the combination is connected to a 100 V supply.Q.16 A 600pF capacitor is charged by a 200V supply. It is then disconnected from the supply and is connected to another uncharged 600 pF capacitor. How much electrostatic energy is lost in the process?Q.17 Two tiny spheres carrying charges 1.5 µC and 2.5 µC are located 30 cm apart. Find the potential and electric field:(a) at the mid-point of the line joining the two charges, and(b) at a point 10 cm from this midpoint in a plane normal to the line and passing through the mid-point.Q.18 The plates of a parallel plate capacitor have an area of 90 cm2 eachand are separated by 2.5 mm. The capacitor is charged by connectingit to a 400 V supply.(a) How much electrostatic energy is stored by the capacitor?(b) View this energy as stored in the electrostatic field between the plates, and obtain the energy per unit volume u. Hence arrive at a relation between u and the magnitude of electric field E between the plates.Q.19 A 4µF capacitor is charged by a 200 V supply. It is then disconnected from the supply, and is connected to another uncharged 2 µF capacitor. How much electrostatic energy of the first capacitor is lost in the form of heat and electromagnetic radiation?Q.20 A spherical capacitor has an inner sphere of radius 12 cm and an outer sphere of radius 13 cm. The outer sphere is earthed and the inner sphere is given a charge of 2.5µC. The space between the concentric spheres is filled with a liquid of dielectric constant 32.(a) Determine the capacitance of the capacitor.(b) What is the potential of the inner sphere?(c) Compare the capacitance of this capacitor with that of an isolated sphere of radius 12 cm. Explain why the latter is much smaller.Q21 An electrical technician requires a capacitance of 2 µF in a circuit across a potential difference of 1 kV. A large number of 1 µF capacitors are available to him each of which can withstand a potential difference of not more than 400 V. Suggest a possible arrangement that requires the minimum number of capacitors.Q.22 A condenser having capacity 2 F is charged to 200V potential, its plates are joined to any resistance wires. What is the heat produced?Q.23 What is the net charge on a charged capacitor?Q.24 What will happen to the capacity of a parallel plate capacitor if area of each plate is doubled and distance between the plates becomes halved?

Q.25 What happens to the electric field inside a dielectric when it is placed in an

external electric field?

Q.26What will be the effect on potential if a medium of dielectric constant K is

introduced?

Q.27 What would be the work done if a point charge +q is taken from a point A to the

point B on the circumference of the circle, which is having a +q point charge at the

centre?

Q.28 a) What is the unit of electric flux?

b) Is it correct that the capacitance of a spherical conductor is equal to the radius

of the conductor in CGS system?

Q.29 Is electric potential necessarily zero at a point where electric field strength is zero.

Q.30Does electric potential increase along electric lines of forces.

Q.31 Four metallic plates each with surface area ‘A’ and interplate separation ‘d’ are placed as shown. Alternate plates are connected to points A and B. What is the equivalent capacitance of the system?

Q.32 Four capacitors are connected as shown in the fig. What is the equivalent capacitances between A and B?

Q.33 If a unit charge is taken from one part to another part over an equipotential surface, then what is the work done on the charge?Q.34 Give the relation between the electric field and potential for closely spaced equipotential surfaces. Q.35 What are equipotential surfaces?Q.36 What principle do we use to find the potential at a point due to a system of charges?Q.37 What is a Vande Graaff Generator? Draw a Vande Graaff generator?Q.38 What is electrostatic shielding? During thunderstorms it is safer to be inside a car or stand under the tree.Explain your answer.Q.39 In a parallel plate capacitor with air between the plates has an area 6*10 -3m2 and the distance between the plates is 6 mm.find the capacitance of the capacitor.if this capacitor is connected to a 200v supply, what is the charge on each plate of the capacitor?Q.40The electric field at a point due to a point charge is 20Nc -1 and the electric potential at that point is 40jc-1.Calculate the distance of the point from the charge and the magnitude of the charge.Q.41 A parallel plate condenser with plate area A is filled with two dielectric K1 and K2 each occupying equal space lengthwise. If the separation between two plates is t for each dielectric then what is the capacity of the condenser.

Q.42 A parallel plate capacitor having a plate separation 2mm possesses a capacitance of 18PF.The capacitor is connected to a 100v supply.Explain what would happen , if a 2 mm thick

mica sheet of dielectric const k=6 were inserted between the plates(a) while the voltage supply remains connected.?(b) after the supply was disconnected.Q.43 What is the potential energy of a dipole placed in an external field? Also give an expression for Torque experienced by the dipole in a uniform electric field. What will be the torque experienced by the dipole if it is in the direction of the electric field?Q.44 A 300PF capacitor is charged by a 200v supply.it is then disconnected from the supply and is connected to another uncharged 300PF capacitor.How much energy is lost in the process? Q.45 Derive the formula for effective capacitance when (i)Capacitors C1 and C2 are connected in series.(ii)Capacitors C1 and C2 are connected in parallel.What happen to the charge on the capacitor if it is disconnected from the battery? Q.46 Differentiate between electrostatic potential and electrostatic potential energy? A metal sphere 0.30 m in radius is positively charged with 2 C. Find the potential at distance 1m from the sphere and at the centre of the sphere. Q.47 Two capacitors C 1 and C 2 are charged to 120 V and 200 V respectively. It is found that by connectingthem together the potential on each one can be made zero. Then :(1) 3C1 5C2 (2) 3C1 5C2 0(3) 9C1 4C2 (4) 5C1 3C2

Q.48 Define electric dipole moment. Write its S.I. unit

Q.49 . Write two limitations of Coulomb’s law.

Q.50. What are the unit and dimensions of permittivity of free space?

Q.51. Calculate the electrostatic force between two α- particles at a distance of 2x10-5m between

them.

Q.52. Why do electric field lines never cross each other?

Q.53. Derive an expression for the electric field at a point on the equatorial line of an electric

dipole.

Q.54. Does an electric dipole always experience a torque, when placed in uniform electric field?

Support your answer with reason.

Q.55. How an electrostatic potential is related to the electric field at a point?

Q.56. No work is done in moving a test charge over an equipotential surface. Why?

Q.57. Derive an expression for the potential energy of an electric dipole in an external uniform

electric field.

Q.58. What is meant by ‘electrostatic shielding’?

Q.59. Derive an expression for the capacitance of a parallel plate capacitor? On what factors

does the capacitance of a parallel plate capacitor depend?

Q.60. Define dielectric constant in terms of the capacitance of a capacitor.

Q.61. In a parallel plate capacitor, how is the capacity affected, when without changing the

charge.

a. The distance between the plates is doubled.

b. Area of the plates is halved.

Q.62. Derive an expression for the energy stored in a parallel plate capacitor with air as the

core material of the capacitor.

Q.63 What does q1 + q2 Signify.

"Om Sai Ram"

Properties of Electromagnetic WavesElectromagnetic waves are composed of oscillating electric and magnetic fields at right angles to each other and both are perpendicular to the direction of propagation of the wave. Electromagnetic waves differ in wavelength (or frequency).In an electronegative wave the electric field E(vector) and the Magnetic field B(vector) oscillate perpendicular to each other and both are perpendicular to direction of propagation of wave.The source that produce them and methods of their detection are different, but they have the following common properties :1. Electromagnetic waves are propagated by oscillating electric and magnetic fields oscillating at right angles to each other.2. Electromagnetic waves travel with a constant velocity of  3 x 108 ms-1 in vacuum.3. Electromagnetic waves are not deflected by electric or magnetic field.4. Electromagnetic waves can show interference or diffraction.5. Electromagnetic waves are transverse waves.

6. Electromagnetic waves may be polarized.7. Electromagnetic waves need no medium of propagation. The energy from the sun is received by the earth through electromagnetic waves.8. The wavelength (λ) and the frequency (v) of electromagnetic wave is related asc = v λ = ω/The S.I. unit of frequency is Hertz.1 Hertz = 1 c / sThe S.I. unit of wavelength is metre.We however, often express wavelength in Angstrom unit [ Ã… ]1 Ã… = 10-10 mAlso, 1 nanometer = l nm = 10-9 m(In the chapter electromagnetic waves, only 1 mark, 2 marks or 3 marks questions will be asked in Board Exams. There is no chance for a 5 marks question. So, we’ve included all in a single section.)1. Discuss the inconsistency in Ampere’s Circuital Law.2. What modification was made to Ampere’s Circuital Law by Maxwell?3. What is displacement current?4. Conduction current and displacement current can be separately discontinuous. But their sum is continuous. Explain.5. Can displacement current (or a changing electric flux induce a magnetic field? Explain6. State the important consequences of displacement current.7. State the important properties of displacement current.8. Write Maxwell’s equations of electromagnetism and state the law underlying each equation.9. Explain what led Maxwell to predict the existence of electromagnetic waves.10. How are electromagnetic waves represented mathematically?11. What is the dimension of (a)μ0 ε0(b)√(μ0 ε0)

12. Discuss how an accelerating charge becomes a source of an electromagnetic wave?13. Describe Hertz’s experiment for producing and detecting electromagnetic waves.14. Explain how Hertz demonstrated the various properties of electromagnetic waves?15. List the different landmarks in the history of electromagnetic waves.16. Prove the transverse nature of electromagnetic waves mathematically.17. Write the properties of electromagnetic waves.18. What is electromagnetic spectrum.19. Name the main parts of the electromagnetic spectrum and mention their frequency range and source of production. Also write their important properties and uses.HOTS QUESTIONS FROM ELECTROMAGNETIC WAVES1. If you find closed loops of magnetic field in a region of space, does it necessarily mean that actual charges are flowing across the area bounded by the loops? Explain.2. Why is it that induced electric fields due to changing magnetic flux are more readily observable than the induced magnetic fields due to changing electric fields?3. A variable frequency AC source is connected to a capacitor. Will the displacement current increase or decrease with increase in frequency?4. Why is the quantity ε0 dφE/dt called displacement current?5. What oscillates in am Electromagnetic Wave?6. Why sound waves are not considered em waves?7. What is the phase relationship between the oscillating electric and magnetic fields in an electromagnetic wave?

8. X- rays and γ rays have a region of overlapping frequencies and have similar characteristics. But why they are treated as different? (OR) How are γ rays different from X rays?9. Why is the ozone layer of atmosphere crucial to the existence of life on earth?10. Why does “RADAR” use microwaves?11. In a microwave oven, the food kept in a closed plastic container get s cooked without melting or burning the plastic container. Explain how?12. Can an electromagnetic wave be deflected by an electric or magnetic field? Justify your answer.13. Name the constituent radiation of electromagnetic spectrum which(a) is used in satellite communication(b)Is used for studying crystal structure(c)is emitted during decay of radio active nuclei(d) is absorbed by ozone layer Write two more uses of each14. What is the dimension of E/B?15. Show that the dimensions of are that of electric current16. he sunlight reaching the earth has a maximum electric field of 810 V/m. What is the maximum magnetic field associated with it?17. Calculate the relative permitivity of a medium of relative permeability 1.0 if the velocity of light through the medium is 2 x 108 m/s.18. Which are the different layers of earth’s atmosphere?Numerical Problems from ELECTROMAGNETIC WAVES for CBSE Class XII1. A parallel plate capacitor has circular plates, each of radius 5.0 cm. It is being charged so that electric field in the gap between its plates rises steadily at the rate of 1012V m-1s-1. What is the displacement current?

2. The voltage between the plates of a parallel plate capacitor of capacitance 1.0 μF is changing at the rate of 5 V s-1. What is the displacement current in the capacitor?3. A parallel plate capacitor has two metal plates of size 30 cm X 15 cm and separated by 2.0 mm. The capacitor is being charged so that the charging current has a steady value of 100 mA. Calculate the rate of change of potential difference between the capacitor plates. What is the displacement current between the capacitor plates?4. The frequencies of radio waves in AM broadcast band range from 0.55 x 106 to 1.6 x 106 Hz. What are the longest and shortest wavelengths in this band?5. A plane electromagnetic wave of frequency 25 MHz travels in free space along X – direction. At a particular point in space and time, E = 6.3 j V/m. What is B at this point?

ample paper class 12 half yearly exam

Q. "Om Sai Ram"

1:Name the experiment for which the following graph, showing the variation of intensity of scattered electrons with the angle of scattering, was obtained.

Q.2: What are the dimensions of magnetic flux? What is the flux associated with a plane coil of area A , having N turns in a uniform magnetic field B ?

Q.3: One billion electrons pass from A to B in a conductor in 1 milli second. What is the direction and magnitude of current?

Q.4: A rectangular current loop is in an arbitrary orientation in an external uniform magnetic field. Is any work required to rotate the loop about an axis perpendicular to its plane? Explain.

Q.5 Define electrical susceptibility. How it is related to dielectric constant.

Q.6 A plane EM wave of frequency 25 Hz travels in free space along X direction. At a Particular point in space and time the electric vector is E = 6.3j V/m. Calculate B at this point.

Q.7 What is the effect on the following on inserting a dielectric in a parallel plate capacitor:

(a) Capacitance (b) Charge on the plates of the capacitor

Q.8State laws which are used for calculating equivalent resistance of unbalanced wheat stone bridge.

OR

Calculate the equivalent resistance of the following circuit.

Q.9: Draw a well labelled diagram to show Earth’s magnetic field and angles associated with it.Q.10: Calculate the current flowing in the following circuit and the heat loss across 2.2 kΩ resistor in 10 seconds. Q11.An inductor L of reactance XL is connected in series with a bulb B to an A.C. source as shown in the figure. Briefly explain how the brightness of the bulb changes when

(a) Number of turns of the inductor is reduced and

(b) A capacitor of reactance XC =XL is included in series in the same circuit.

Q.12:Draw hysteresis loops for soft iron and steel. Hence, explain why soft iron is used

for preparing electromagnets while steel is used for preparing permanent magnets.

Q.13: (a) The coefficient of mutual induction of the two coils is 0.5 H. If the current is increased from 2 to 3 A in 0.1 seconds in one of them, then find the induced EMF in the second coil. (b) Give two advantages of eddy currents in electrical appliances.

Q. 14: The dielectric strength of air is 3 x 106 V/m. What is the maximum charge that can be safely stored on a sphere of radius 10m?

Q.15:An electron is moving at 106 m/s in a direction parallel to a current of 5 A flowing through an infinitely long wire at a perpendicular distance of 10 cm in air. Calculate the magnitude of force experienced by an electron.

Q. 16. An alpha particle and a proton accelerated by the same potential difference enter into a magnetic field. Find the ratio of their radius and the ratio of their frequency.

Q.17: (a) Does every charge give out electromagnetic waves? Explain very briefly.

(b) The magnetic field in a plane EM wave is given by

By = 2 × 10 -7 sin (0.5 × 103 z + 1.5 × 1011 t) T.

(i) What is the frequency of the wave?

(ii) Write an expression for the electric field.

Q.18: Use Kirchhoff’s laws to find the currents I1, I2 and Ig in Wheatstone bridge

shown in figure.

Q.19: A conductor of length l is connected to a dc source of emf V. if the length of the conductor is tripled by stretching it, keeping V constant, explain how do the following factors vary in the conductor:

(1) Drift speed of electron (2 ) Resistivity

Q.20: (a) Distinguish between resistance, reactance and impedance for an AC circuit.

(b) What do we mean by the term phasors? Draw a phasor diagram for an AC circuit with a capacitor.

Q21.X -ray of wavelength λ falls on photosensitive surface emitting electron. Assuming that the work function of the surface can be neglected, prove that de-Broglie wavelength of electron emitted will be [ h λ/2mc]1/2.

Q.22: Two parallel conductors are carrying current I1 and I2 are kept ‘r’ distance apart. Deduce an expression for force unit length acting between them. Define one ampere using this relation.

Q.23: Draw a circuit diagram for a potentiometer circuit used to find internal resistance of a cell and deduce the expression for internal resistance in terms of the balancing lengths.

Q.24:Sketch the graphs, showing the variation of stopping potential with frequency of incident radiations for two photosensitive materials A and B having threshold frequencies ƒ1 > ƒ2 respectively. (1) Which of the two metals A Or B has higher work function? (2) Will the slope of both curves be same? Justify your answer.

Q.25: State Lenz’s law. Two identical metallic rods one of copper and another of aluminum are rotated with same angular speed w in presence of same magnetic field. In which case (1) the induced emf (2) the induced current, will be more and why?

Q.26: State the principle of working of galvanometer. In galvanometer (i) concave shaped poles are used (ii) phosphor-bronze alloy is used for the suspension wire. Explain why? The current sensitivity of moving coil galvanometer is 5 divisions/mA and voltage sensitivity is 20 division/volt. Calculate the resistance of galvanometer.

Q.27: In L-R series circuit, the potential difference across the inductor ‘L’ and the resistor ‘R’ are 120 V and 90 V respectively and rms value of current is 3 A (1) calculate r.m.s voltage across the circuit. (2) Is the algebraic sum of the voltage across two components

more than the applied voltage? If yes, explain the reason (3) Calculate the phase angle between the voltage and current.

OR

A resistor of resistance 400Ω, and a capacitor of reactance 200Ω,are connected in series to a 220V,50Hz a.c. source .If the current in the circuit is 0.49 ampere find the (i) voltage across the resistor and capacitor(ii) value of inductance required so that voltage and current are in same phase.

Q.28: Explain the effect of introducing a dielectric slab between the plates of a parallel plate capacitor on its capacitance. Derive an expression for its capacitance with the dielectric slab, what is the effective capacitance across XY of the capacitor of capacitance if the capacitor with air/vacuum between the plates of area A each and distance d apart was Co.

OR

State gauss theorem in electrostatics. Derive an expression for the electric field strength near an infinite plane sheet of charge. A point charge of +10μC is at a distance 5cm directly above the centre of a square of side 10cm as shown in the figure. What is the magnitude of electric flux through the square?

Q.29: With the help of a labeled diagram explain the construction and working of an a.c.

generator. Deduce the expression for emf induced. What is average and root mean

square value of emf induced ?

Q.30: (a) Give two advantages of the presence of a soft iron core in a moving coil galvanometer.

(b) How can you turn a galvanometer into a voltmeter? Give the necessary equation.

(c) A galvanometer having a coil resistance 100 Ω gives a full scale deflection when a current of 1 mA is passed through it. What is the value of the resistance which can

convert this galvanometer into a meter giving full scale deflection for a potential difference of 10 V?