KENDRIYA VIDYALAYA RWF, YELAHANKA NEWTOWN BANGALORE MODEL PAPER-1 BLUE PRINT

PHYSICS

S.no Name of the Unit VSA (1) SA II (2) SA I (3) LA (5) Total1 Electrostatics 1(1) 4(2) 3(1) --- 8(4)2 Current electricity --- 4(2) 3(1) --- 7(3)3 Magnetic effects of current 1(1) 2(1) --- 5(1) 8(3)4 Electromagnetic induction &

a.c--- --- 3(1) 5(1) 8(2)

5 Electromagnetic waves 1(1) 2(1) --- --- 3(2)6 Optics 2(2) 4(2) 3(1) 5(1) 14(6)7 Dual nature of radiation and

matter1(1) --- 3(1) --- 4(2)

8 Atoms and Nuclei 1(1) 2(1) 3(1) --- 6(3)9 Electronic devices 1(1) --- 6(2) --- 7(3)10 Communication systems --- 2(1) 3(1) --- 5(2)

Total 8(8) 20(10) 27(9) 15(3) 70(30)

KENDRIYA VIDYALAYA RWF, YELAHANKA NEWTOWN BANGALORE MODEL PAPER-1

PHYSICS

CLASS XII TIME ALLOWED 3hrs M.M 70

GENERAL INSTRUCTIONS: -

1. All questions are compulsory.2. There are 30 questions in total. Questions 1 to 8 carry one mark each, questions 9 to 18 carry two marks

each, questions 19 to 27 three marks each and questions 28 to 30 carry five marks each.3. There is no overall choice. However, an internal choice has been provided in one question of two marks,

one question of three marks and all three questions of five marks each. You have to attempt only one of the choices in such questions.4. Use of calculators is not permitted.5. You may use the following values of physical constants wherever necessary :

c = 3 x 108 m/sh = 6.626 x 10-34 Jse = 1.602 x 10-19 Cµo = 4π x 10-7 T-m/A

14 πεo

= 9 x 109 N m2/C2

6. You have been allotted 15 min time to read this question paper apart from 3 hrs to solve it._______________________________________________________________________________________

(1) What is the ratio of the electrostatic force experienced by an electron and an α- particle separately in a uniform electric field of intensity 5.0 N/C? (1)(2) “Magnetic field lines form closed loops where as electric field lines do not.” Why? (1)(3) Why are microwaves used in Radar? (1)(4) A convex lens of refractive index nl is immersed in a medium of refractive index nm. How will the lens behave if (a) nl > nm (b) nl < nm (1)(5) Give any one point of difference between interference and diffraction. (1)(6) What is the de- Broglie wavelength (in Ao) associated with an electron accelerated through a potential difference of 900 V? (1)(7) The following is the sequence of radioactive isotope decay of an isotope ‘D’. If the mass number and atomic number of D2 are 176 and 71 respectively find the mass number and the atomic number of ‘D’?

(1)

(8) Draw the symbolic representation of a pnp – transistor. (1)(9) Derive an expression for the electric field intensity at the centre of an electric dipole. (2)(10)Find the equivalent capacitance of the following network of capacitors between the ends A and C? (2) (11)A conducting wire of length ‘l’ , area of cross section ‘A’ , resistance ‘R’ and resistivity ‘ρ’ is stretched to ‘n’ times its original length. Show that the new resistance could be n2R. (2) OR Length of a conductor is increased to 3 times. What is the effect on (i) drift speed of electrons and (ii) resistivity if the potential difference across the conductor is kept constant.(12) A voltage of 30 V is applied across a carbon resistor with first, second and third rings of blue, black and yellow respectively. Calculate the current in mA through it? (2)(13)Using Ampere’s circuital law, derive an expression for the magnetic field along the axis of a toroidal solenoid. (14)State any four characteristic properties of electromagnetic waves. (2)

(15) The distance between two lenses of an astronomical telescope in normal vision is 100 cm and its magnification is 19. Find the focal lengths of the objective lens and the eye piece? (2)

(16)Draw the resulting wave front in the following cases. (2)(17)Derive an expression for the total energy of an electron in any orbit of a Hydrogen atom according to

Bohr’s atomic model. (2)(18)Draw the block diagram of a communication system. What is meant by detection of a modulated carrier

wave? Describe briefly the essential steps involved in detection? (2)(19)A conducting slab of thickness‘t’ is introduced, without touching, between the plates of a parallel plate

capacitor, separated by a distance‘d’. Derive an expression for the capacitance of the capacitor when t < d and hence deduce expression for capacitance when t = d? (3)

(20)The length of potentiometer wire is 600 cm and it carries a current of 40 mA. For a cell of emf 2 V and internal resistance 10 Ω, the null point is found to be at 500 cm. If a voltmeter is connected across the cell, the balancing length is decreased by 10 cm. Find

(i) the resistance of the whole wire (ii) resistance of the voltmeter and (iii) reading of the voltmeter? (3)

(21)A pure inductor is connected across an a.c source. Show mathematically that the current in it lags behind

the applied emf by a phase angle of π2 . Also draw the variation of inductive reactance with the

frequency of a.c source. (3) OR A pure capacitor is connected across an a.c source. Show mathematically that the current in it

leads the applied emf by a phase angle of π2 . Also draw the variation of capacitive reactance with the

frequency of a.c source.(22)An object kept in front of a concave mirror forms an image double the size of the object. If the focal length

of the mirror is 20 cm, calculate all possible object distances? (3)(23)Red light, however intense it is, cannot produce the emission of electrons from a clean zinc surface. But

even weak ultra violet radiation can do so. Why? ORX- rays of wavelength ‘λ’ fall on a photo sensitive surface, emitting electrons. Assuming that the wave function of the surface can be neglected, prove that the de – Broglie wavelength of the electron emitted

will be √ hλ2mC

where the symbols stand for their usual meaning. (3)

(24)Draw the binding energy curve for different nuclei. Explain with the help of this graph, the release of energy in the process of nuclear fusion? (3)

(25)The following truth table gives the output of two input logic gate.

A B Output0 0 10 1 01 0 01 1 1

i. Identify the logic gate used and draw the logic symbolii. If the output of this gate is fed to a ‘NOT’ gate, name the new logic gate so formed. (3)

(26) What is a Zener diode? How it is symbolically represented? With the help of a relevant circuit diagram, explain the use of Zener diode as a voltage stabilizer? (3)

(27) What is modulation? Explain the need of modulating a low frequency information signal. With the help of relevant diagrams, differentiate amplitude modulation and frequency modulation? (3)

(28) State Biot- Savart law. Using this law, obtain an expression for the magnetic field induction at a point situated on the axis of a current carrying circular coil and hence deduce an expression for the same at the centre of the coil? (5)

OR Draw a neat labeled diagram of a Cyclotron. State the underlying principle and explain how a positively

charged particle gets accelerated in this machine? Show mathematically the Cyclotron frequency does not depend upon the speed of the particle.

(29) State the condition for resonance to occur in series RLC a.c circuit and derive an expression for the resonance frequency. Draw a plot showing the variation of the peak current with frequency of a.c source used. Define Quality factor, Q of the circuit. Calculate the impedance and wattles current of the given circuit? (5)

OR A metallic rod of length ‘l’ is rotated at a constant angular speed ‘ω’, normal to a uniform magnetic

field ‘B’. Derive an expression for the current induced in the rod if the resistance of the coil is ‘R’?

A circular coil of radius 8.0 cm and 20 turns rotates about its vertical diameter with an angular speed of 50 s-1 in a uniform horizontal magnetic field of magnitude 3 x 10 -2 T. Find the maximum and the average values of emf induced in the coil?

(30) What do we understand by “Polarization of a wave”? How does this phenomenon help us to decide whether a given wave is transverse or longitudinal in nature? Briefly explain a method to produce polarized light?

Two Polaroid are placed at 90o to each other and the intensity of the transmitted light is zero. What will be the intensity of the transmitted light when one more Polaroid is placed between these two bisecting the angle between them? Take the intensity of the unpolarized light as Io. (5)

OR What is interference of light? Write two essential conditions for sustained interference pattern to be

produced on the screen. Draw a graph showing the variation of intensity versus the position on the screen in Young’s double slit experiment when (a) both slits are open and (b) one of the slits is closed.

What will be the effect on the interference pattern in Young’s double slit experiment when (i) Screen is moved closer to the plane of the slits(ii) The original source is moved closer to the plane of the slits?

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KENDRIYA VIDYALAYA RWF, YELAHANKA NEWTOWN BANGALORE MODEL PAPER-1

CLASS XII PHYSICS MARKING SCHEME

Q.No Value points Marks1 F = Eq F1/F2 = q1/q2 = ½ 1:2 ½ +½2 Magnetic monopoles do not exist and isolated electric charges exist ½ + ½3 Microwaves have shorter wavelengths and suffer minimum deviation and can be beamed

directly to the target.1

4 (i) Convex (Converging) (ii) Concave(Diverging) ½ + ½

5 Any one point each ½ + ½6 λ = 12.27/√ V Ao = 12.27/√ 900 = 12.27/30 = 0.409 Ao ½ +½7 Mass Number = 180 Atomic Number = 72 ½ + ½8 Correct symbol + Direction of flow of conventional current ½ + ½9 Diagram showing the direction of electric field +correct derivation ½ +1½10 Correct analysis of series and parallel capacitors + Substitution & calculation C = 5/2 µF 1 + 111 R1 = ρl1/A1 & R2 = ρl2/A2 ; R2/R1 = l2/l1 x A1/A2 ; l2 = nl1 & A2 = A1/n ; R2 = n2 R1 OR

Vd = eE/m x τ ; Vd = eV/ml x τ and Vd’ = eV/mx3l xτ ; Vd’ = Vd/3 Drift velocity reduces by 3 times.R = ρl/A and R’ = ρl’/A’ ; R’ = 9R ; Resistance increases by 9 times

½+½+½+½ OR½+½

½+½12 Correct colour code ( 60 x 10 4 Ω ) ; I = V/R and Substitution + calculation 1 +½ +½13 Ampere’s circuital law statement and diagram + Required Derivation ½ +½ +114 Any four correct properties ½+½+½+½15 m = fo/fe & fo + fe = L ; substitution + calculation of fo = 95 and fe = 5 ½+½+½+½16 Correct diagrams after reflection or refraction ½ x 4 = 217 Diagram + correct derivation ½ +1½18 Block diagram +meaning of detection + Steps involved in detection ½+½+ 119 Diagram + derivation for t < d + deducing the formula for t = d 1 + 1½ +½20 E1/E2 = l1/l2 & correct substitution to calculate E1 = 2.4 V

(i)Resistance of the wire R = V/I = 60Ω(ii)r = (l1 – l2)/l2 x R where l2 = 500 – 10 = 490cm ; calculation of R = 490Ω

½+½½½

(iii)r = ( E- V )/V x R and calculation of V = 1.96 Volts ½ +½21 Correct mathematical proof of phase difference between current and voltage in an inductor

and graph of source voltage vs inductive reactance ORCorrect mathematical proof of phase difference between current and voltage in an capacitor and graph of source voltage vs capacitive reactance

2 + 1

2 + 1

22 1/f = 1/u + 1/v and m = -v/uSubstituting m= -2 for real image and m = +2 for virtual imageSubstitution of f and correct v for calculating u = - 30cm for real and -10cm for virtual

½ +½½ + ½½ +½

23 Correct reason + proof i.e hν = ½ mv2 i.e hc/λ = ½ mv2 ;from this v = √2 hc /mλ ; But de –Broglie wavelength λ = h/mv ; now substitute for v

1½+½+½+½

24 Binding energy curve with correct labeling of axes and showing a few (at least 4) nuclei on the curve and explanation for nuclear fusion on the basis of the curve

2 + 1

25 (i)NOR gate identification and logic symbol for NOR gate(ii)NOR + NOT = OR

1 + 11

26 Meaning of Zener diode + correct symbolCorrect circuit diagram and correct explanation

½ + ½1 + 1

27 Definition of modulation + need for modulation + diagrams of message , AM & FM ½ + 1 +½+½ +½

28 B-S law statement (mathematical)Diagram of circular coil with a point on the axis and direction of dB and labelingDerivation + deducing the formula at the centre ORLabelled diagram of Cyclotron + principle + working + independence of frequency on ‘v’

½½ + ½3 + ½

1+½+1½+2

29 Conditions for resonance + RLC – series circuit with a.c source +deriving condition for resonance + frequency of a.c source vs current graph + Q- factor definition + deriving formula for impedance and wattles current. ORDiagram showing the direction of B and rotation of the rodDeriving e = ½ Bω2lAnd I = e/Reo = NBAω substitution and calculation of eo

eavg = 0 (For every positive half cycle ther is a corresponding negative half cycle)

1+½+1+½+½+1+½

½2½1½

30 Meaning of polarization + transverse waves alone undergo polarizationMethod of producing polarized light by reflection or any other method

½+½2

Solution to the numerical using I = Io cos2 Ø ORMeaning of Interference + Conditions for sustained Interference ( any two)Intensity distribution graph for Interference and diffraction β= λ D/d(i)Fringe width decreases as D decreases (ii)No interference observed as S/s < λ/D may not be satisfied.

2

½+1½+½½½½1

KENDRIYA VIDYALAYA RWF, YELAHANKA NEWTOWN BANGALORE MODEL PAPER-2 BLUE PRINT

PHYSICS

S.NO UNITS VSA(1MARK)

SA I(2 MARKS)

SAII(3 MARKS)

LA(5 MARKS)

TOTAL

1. Electrostatics 2(1) 6(2) 8(3)2. Current Electricity 1(1) 6(2) 7(3)3. Magnetic effect of

current and Magnetism

1(1) 2(1) 5(1) 8(3)

4. Electromagnetic Induction and A.C

1(1) 2(1) 5(1) 8(3)

5. Electromagnetic Waves

1(1) 2(1) 3(2)

6. Optics 1(1) 2(1) 6(2) 5(1) 14(5)7. Dual Nature of

Matter4(2) 4(2)

8. Atoms and Nuclei 1(1) 2(1) 3(1) 6(3)9. Electronic Devices 1(1) 6(2) 7(3)10. Communication

Systems1(1) 4(2) 5(3)

TOTAL 8(8) 20(10) 27(9) 15(3) 70(30)

Note: Figures outside the brackets indicate marks and inside indicates number of questions.

WEIGHTAGE TO DIFFICULTY LEVEL OF QUESTIONS

S.NO Estimated difficulty level of questions Percentage of marks1. Easy 15

2. Average 703. Difficult 15

KENDRIYA VIDYALAYA RWF, YELAHANKA NEWTOWN BANGALORE MODEL PAPER-2

CLASS: XII TIME: 3 HOURS MAX.MARKS: 70 SUB: PHYSICS

General instructions:

(a) All questions are compulsory.(b) There are 30 questions in total. Questions 1 to 8 carry one mark each,

questions 9 to 18 carry two marks each, questions 19 to 27 carry three marks each and questions 28 to 30 carry five marks each.

(c) There is no overall choice. However, an internal choice has been provided in one question of two marks, one question of three marks and all three questions of five marks. You have to attempt only one of the given choices in such questions.

(d) Use of calculator is not permitted.(e) You may use the following physical constants. C=3×108 ms-1

h=6.6×10 -34 Js e=1.6×10-19 C µ0=4π×10-7TmA-1

1/4πε0= 9×109 Nm2C-2

Avogadro’s number NA= 6.023×1023/mole Mass of the neutron mn = 1.67 ×1027 Kg. Mass of the electron me = 9.1×10-31 Kg. Radius of the earth = 6400 Km.----------------------------------------------------------------------------------------------------------------------

1. You are asked to measure emf of a cell. Which instrument will you use -- a high resistance voltmeter or a potentiometer and why?

2. Under what condition does an electron moving through a magnetic field experience maximum force?

3. A bar magnet falls from a height ‘h’ through a metal ring. Will its acceleration be equal to g? Give reason for your answer.

4. When light undergoes refraction, what happens to its frequency?5. What is the ratio of speed of infrared rays and ultraviolet rays in vacuum?6. Compare the radii of two nuclei with mass numbers 1 and 27 respectively.7. Draw energy band diagram of a P- type semiconductor.8. Write the frequency band of FM radio broadcast. 9. A parallel plate capacitor with air between the plates has a capacitance of

8pF. The separation between the plates is now reduced by half and the space between them is filled with a medium of dielectric constant 5. Calculate the value of the capacitance of the capacitor in the second case.

10.Name two elements of earth’s magnetic field other than horizontal components of earth’s magnetic field. Why do we say that at places like Delhi and Mumbai, a magnetic needle show that true north directions quite accurately as compared to the other places in India.

11.You are given an air core coil, a bulb, an iron rod and a source of electricity, suggest a method to find whether the given source is dc or ac.Explain your answer.

12. In a plane electromagnetic wave, the electric field oscillates sinusoidally at a frequency of 2.0×1010 Hz and amplitude 48 V/M.

a. What is the wavelength of the wave? b. What is the amplitude of the oscillating magnetic field?

13.The following data was recorded for values of object distance and the corresponding values of image distance in the experiment on study of real image formation by a convex lens of power +5D.One of these observations is incorrect. Identify this observation and give reason for your choice:

S.NO 1 2 3 4 5 6Object distance(cm) 25 30 35 45 50 55Image distance (cm) 97 61 37 35 32 30

14. An α-particle and a proton are accelerated from the state of rest through the same potential difference V. Find the ratio of de Broglie wavelengths associated with them.

15.Write the Einstein’s photoelectric equation in terms of the stopping potential and the threshold frequency for a given photosensitive material. Draw a plot

Showing the variation of stopping potential versus frequency of incident light. 16. In Bohr’s theory of hydrogen atom, calculate the energy of the photon emitted

during a transition of the electron from the first excited state to the ground state. (OR) A radioactive isotope has a half-life of 5 years. After how many half-lives is Its activity reduced to 3.125% of its original activity?

17. Draw the block diagram of a communication system? 18. Explain shortly the need of modulation? 19. State Gauss’ theorem. Using it deduce an expression for the electric field Intensity at any point due to a thin, infinitely long wire of charge/length λ C/m. 20. Define the term ‘electric dipole moment’. Write its SI unit. Derive an expression for the maximum torque acting on an electric dipole, When placed in a uniform electric field.

21. Two cells of emf 1.5V and 2V 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.

(a) Draw the circuit diagram. (b) Using Kirchhoff’s laws, calculate the current in each branch of the circuit and the potential difference across the 5 ohm resistor. 22. Two students X and Y perform an experiment on potentiometer separately Using the circuit diagram shown below. Keeping other things unchanged

(i) X increases the value of resistance ‘R’ (ii) Y decreases the value of resistance ‘S’ in the setup. How would these changes affect the position of the null point.

23. Draw a ray diagram showing how the final image of a distant object using an astronomical telescope is formed in the normal adjustment position. Write the mathematical expression for its magnifying power. Write two distinct advantages of a reflecting type telescope over refracting type telescope.

24. State Huygens’ Principle. For reflection of a plane wave front at a plane reflecting surface, construct the corresponding reflected wave front. Using this diagram, prove that angle of incidence is equal to angle of reflection.

25. A neutron is absorbed by a Li63 nucleus with the subsequent emission of

an alpha particle.(I) write the corresponding nuclear reaction.(II) Calculate the energy released in Mev in this reaction.

Given: mass (Li63) = 6.01512126u; mass (neutron) = 1.0086654u;

Mass (alpha particle) = 4.0026044u and mass (triton) = 3.01000000u Take 1u = 931Mev/c2.

26. With the help of a circuit diagram explain how a zener diode can be used as a Voltage regulator? (OR) Explain with the help of a circuit diagram the working of n-p-n transistor as a

Common emitter amplifier? 27. Draw the output wave form at X, using the given inputs A, B for the logic Circuit shown below. Identify the gate and also give its truth table?

28. Explain the principle and working of a cyclotron with the help of a neat diagram. Derive the expression for cyclotron frequency. (OR) With the help of a neat labelled diagram explain the principle and working of a Moving coil galvanometer. Prove that in radial magnetic field, the deflection of

the coil is directly proportional to the current flowing in the coil.

29. Distinguish between reactance and resistance. An alternating emf is applied across a capacitor. Show mathematically that current in it leads the applied emf by phase angle of π/2. What is capacitive reactance of such a circuit? Write the unit of capacitive reactance. Draw a graph showing the variation of capacitive reactance with the frequency of alternating current. (OR) What is meant by impedance? Give its unit. Using a phasor diagram derive the expression for the impedance of an a.c. circuit containing L, C and R in series. Find the expression for resonant frequency.

30. Explain the phenomenon of diffraction of light at a single slit, to show the formation of the diffraction fringes. Show graphically the variation of intensity with angle in the single slit diffraction pattern. Derive an expression forthe fringe width of the central maxima. (OR)(i)State two essential conditions for observing sustained interference of light.(ii)Draw the diagram showing intensity distribution of light on the screen for the interference of light in Young’s double slit experiment.(iii)How does the fringe width in the interference pattern change, when the Whole apparatus is immersed in a liquid of refractive index 4/3?

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KENDRIYA VIDYALAYA RWF, YELAHANKA NEWTOWN BANGALORE MODEL PAPER-2

CLASS XII PHYSICS MARKING SCHEME

1. Potentiometer 1/2 It doesn’t draw any current 1/2

2. When the electron moves perpendicular to the magnetic field. 1

3. No. It will be less than g. 1/2 Due to induced current in the ring will oppose the approach of the magnet. (Lenz’s law) 1/24. The frequency remains unchanged. 1

5. 1:1 1

6. R1/R2 =(A1/A2)1/3 1/2 = (1/27)1/3= 1/3 1/2 7. For correct drawing 1

8. 88 to 108 MHz. 1

9. C1= ε0A/d = 8PF 1/2 d’= d/2 1/2 C2= K ε0A/d’ = 80 PF 1

10. Angle of declination and angle of dip 1 At Delhi and Mumbai the angle of declination is very small that is 41 min and 58 min that is why magnetic needle shows true north direction. 1

11. Explaining the conditions for ac and dc source 1 For correct reasoning 1

12. a. Wavelength λ = 3×108 / 2.0×1010 = 1.5×10-2 m 1 b. B0 = 48 / 3×108 = 1.6 × 10 -7 tesla 1 13. f=1/P=.20m=20 cm 1/2 Observation 3 is incorrect 1/2 Correct reason 1 14. λ = h/√2mev 1/2 For α-particle m=4mp, e=2e 1/2 After substituting getting λα: λp = 1: 2√2 1

15. For writing the equation 1 For drawing the graph 1

16. En = -13.6/n2 ev 1/2 E1 = -13.6/1=-13.6 ev 1/2 E2 = -13.6/4=-3.4 ev 1/2 Energy of photon emitted = 10.2 ev 1/2 (OR)

R/R0 = (1/2)n 1/2 R/R0 = 3.125/100 1/2 For finding n =5 1 17. For drawing correct diagram 2 18. Height of the antenna, Power radiated &mixing up of signals 2 19. For writing the theorem 1 Correct derivation with drawing 2

20. For writing correct definition and unit 1 For correct derivation with proper diagram 2

21. Drawing correct circuit diagram with directions of current 1 Currents through branches are 1/34, 9/34, 10/34 A 1&1/2 Potential difference = 25/17 V 1/2

22. Balancing point (null point) shifts towards B with correct reason 1&1/2 Balancing point (null point) shifts towards A with correct reason 1&1/2

23. Correct ray diagram with m = - fo/fe 1&1/2 Writing two advantages 1&1/2 24. For writing Huygens’ Principle 1 For drawing correct diagram 1 For proving angle i= angle r 1

25. For writing the correct equation 1 Calculation of mass defect = 0.011187u 1 Energy released = 10.415 Mev 1

26. Circuit diagram 1 Proper explanation 2 (OR) Circuit diagram 1 Proper explanation 2

27. For identifying the Gate 1 For drawing the out put waveform and writing the truth table 2

28. Principle 1 Diagram 1 Working 1 Expression for cyclotron frequency 2 (OR)

Principle 1 Diagram 1 Working 1 Proving α is proportional to I 2

29. Distinguishing 1 For the proof of current leads the voltage by π/2 2 Capacitive reactance with unit 1 Correct graph 1 (OR) Impedance and its unit 1 Phasor diagram with expression for impedance 2 & 1/2 For finding resonance frequency 1 & 1/2

30. Explanation of diffraction at single slit with diagram 2 Intensity variation graph 1 Expression for fringe width of central maxima 2 (OR) Two conditions for sustained interference 2 Intensity variation graph 1 New fringe width = old fringe width /µ 1 As µ of the liquid is 4/3 the fringe width decreases. 1

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KENDRIYA VIDYALAYA RWF, YELAHANKA NEWTOWN BANGALORE MODEL PAPER-3

Class – XII Subject – PhysicsTime: 3 Hrs Marks: 70

General Instructions:1. All questions are compulsory.2.Questions 1 to 8 carry one mark each, questions 9 to 18 carry two marks each, questions 19 to 27 carry three marks each and questions 28 to 30 carry five marks each.3. There is no overall choice. However, an internal choice has been provided in one question of two marks, one question of three marks and all three 4.questions of five marks each. You have to attempt only one of the given choices in such questions. 5. Use of calculator is not permitted.You may use the following physical constants wherever necessary: c = 3 x 10 8 m/s h = 6.6 x 10 -34 Js e = 1.6 x 10-19 C μ 0 = 4π x 10 7 T m /A Boltzman constant K= 1.38 x 1023 J/K Avogadro’s number N A = 6.023 x 10 23 / mole Mass of neutron m n = 1.6 x 10-27 kg--------------------------------------------------------------------------------------------------1. Three capacitors C1 = C2 =C3 = 1μF are connected as shown in the figure. Calculate equivalent capacitance between A and B.

2. A carbon resistance has three colours blue, yellow and red respectively. What will be the resistance?

3. The pole of a magnet is brought near to a stationary charge. What will be the force experienced by pole?

4. What is the ratio of speed of infrared and ultraviolet rays in vacuum?5. How does the self inductance of a coil change, when Number of turns in the coil is decreased?

6 Draw the wavefront coming out of convex lens when a point source of light is placed at its focus

7. If the intensity of incident radiation on a metal is doubled what happens to the K.E of electrons emitted?

8. Compare the radii of two nuclei with mass number 1 and 27 respectively.

9. Keeping the voltage of the charging source constant, what would be the percentage change in the energy stored in a parallel plate capacitor if the separation between its plates were to be decreased by 50%?

10.The vertical component of earth’s magnetic field at a given place is √3 times its horizontal component. If the total intensity of earth’s magnetic field at a place is 0.4 G ,find the value of horizontal component of earths field and angle of dip.

11.A wire of length L is bent in the form of a coil having N turns of same radius. If a steady current I flow through it in a clockwise direction, find the magnitude and direction of the magnetic field produced at its centre.

12.Describe Hertz’s experiment for the production of electro magnetic waves OR

What is the source of displacement current? Write three properties of electromagnetic waves.

13 In the circuit shown bellow W represents an electric bulb. If the frequency ‘f’ of the supply is doubled, how should the values of C and L be changed so that the glow in the bulb remains unchanged?

14.A circular coil having 20 turns, each of radius 8cm is rotating about its vertical diameter with speed of 50 radians per second in a uniform horizontal magnetic fiend of magnitude 30mT.Obtain the maximum average and rms values of the emf induced in the coil.

15. Velocity of light in glass is 2 x 108 m/s and in air is 3 x 108 m/s. If the ray passes through glass to air, calculate the value of critical angle.

16 A radioactive nucleus undergoes a series of decay according to sequence β ά ά

If the mass no and atomic no of A3 are 172 and 69, what is the atomic and mass no of A?

17.A T V Tower has a height of 400m at a given place. Calculate its coverage range, if radius of the earth is 6400 km

18.Idetyfy the logic gate X and Y Give the output wave form if A and B are the two input wave form

19. For the network shown in the figure determine the value of R and current through it, if the current through the branch AO is zero.

20. Explain principle of potentiometer. How it can be used to compare emf’s two primary cells.

21.Find the force between two infinitely long straight conductor carrying current in the same direction.

22. Calculate B.E per nucleon of alpha particle. Given, mass of proton = 1.0073amu, mass of neutron = 1.0087amu and mass of alpha particle = 4.0015amu

23. When a circuit element X is connected across an a.c source a current of √2 A flows through it and this current is in phase with the applied voltage. When another element Y is connected across the same a c source the same current flows in the circuit but leads the voltage by л/2 radians.i. Name the circuit elements X and Y

ii. Find the current that flows in the circuit when the series combination of X and Y is connected across the same voltage.

24.Draw labeled ray diagram of compound diagram. Write the expression for magnifying power and resolving power of microscope ORState and explain Huygen’s principles. On the basis of Huygen’s principles prove laws of reflection

25.The refractive index of the material of a concave lens is n. It is immersed in a medium of refractive index n1 . A parallel beam of light is incident on the lens. Trace the path of the emergent rays in each of the following cases: (a) n1 > n

(b) n1 < n(c) n1 = n

26. Describe Davission and Germer experiment to depict the wave nature of electron

27. (a) Draw the block diagram of a communication system (b) What is meant by ‘ detection’ of a modulated carrier wave? Describe briefly the essential steps for detection.

28. Explain with the help of a circuit diagram, the working of npn transistor as a common emitter amplifier. What is the phase relation between input and output of the CE amplifier? OR

i) Draw I-V characteristics of zener diode and explain significance of breakdown voltage.ii) Explain briefly, with the help of a circuit diagram, how a p-n junction diode works as full wave rectifier.

29. Derive Len’s makers formula. The radii of curvature of a double convex lens are 15cm each. If refractive index of material of lens is 1.5 find focal length of the lens. ORDerive an expression for the refractive index of the prism in terms of angle of prism and angle of minimum deviation.

30.Describe the principle, construction and working of the VanDe Graff generator ORState Gauss’s theorem Using Gauss theorem derive the value of electric field due to an infinite sheet of charge having charge density σC/m2 .Draw a graph showing the variation of electric field with distance R

MARKING SCHEME

Q NO STEP MARKS

TOTAL MARKS

1 C1 +C2 +C3 = 3μF 1 12 64 x 10 2Ω 1 13 The force will be zero as the stationary charge

Particle does not produce any force.1

1

4 1:1 1 15 L α n2 => L is decreased. ½+½ 16 1

1

7 No change in KE 1 18 R œ A 1/3 = 1:3 ½+½ 19 U=1/2 C V 2

C = Aε / d U’ = 2U% increase = U’/ U *100 =200%

½½½½

2

10 Tan Ө = V/H = √3 , Ө = 60As V = √3H andB2 = V2 + H2 = 3H2 + H2 = 4H2

(0.4)2 = 4H2 thereforeH = 0.2 G

½½½½

2

11 2ПRN =L ½ 2

R = L/ 2ПN B= μNI /R = μ2ПN2I /L

½½½

12 Diagram Explanation ORTime varying electric flux Any three properties

11

11

2

13 For the same current value the total impedance must remain same XL –XC must remain same. Thus L and C must both halved simultaneously.

1

1 2

14 Maximum emf induced E0 = NWAω = 0.63 Volt E rms = E0 /√2 = 0.42VAverage emf is zero

½½½

½

2

15 sinC = 1/μ =1/2 C = 30 0

1½½

2

16 Mass no =180 Atomic No = 72

11 2

17 D = √2 RH & Sub = 71.55km

11 2

18 X- NAND Y- NOT Truth table

11 2

19 P/Q = R/S Balanced bridge R = 6Ω Equivalent resistance = 2+2=4Ω Current through 6 Ω is 0.5A

½1½1

3

20 Principle Circuit diagramExplanation with formula E1/E2 = l1 / l2

111

3

21 Diagram Derivation of B= (μo/4π)2I/r F=(μo/4π) 2I1I 2 /r

111

3

22 Mass defect BE = 28.4MeV

11

3

BE/A = 7.1 MeV 123 X – Resistance

Y - CapacitorE/R = √2 AR = XcI = E/Z = E/√R2+ Xc 2

=E/R√2 = 1.0A

½½½½½½

3

24 Ray diagramFormula for magnifying power and R PORPrincipleDiagramLaws of reflection

2½+½

111

3

25 Each ray diagram for (a) n1 > n (b) n1 < n

(c) n1 = n

111

3

26 Diagram Experimental graph Explanation

111

3

27 Block diagram Detection meaning Essential steps (any two)

111

3

28 circuit diagram Explanation Phase relation OR I-V characteristic Explanation Circuit diagram Explanation

221

111½1½

5

29 Ray diagram Derivation 1/f = (μ2 / μ1- 1) ( 1/ R1 – 1/ R2) Substitution = 15 cm OR Ray diagram and labeling

1211

1 ½1+11 1/2

5

Expression for A and Dm Expression for R I

30 Principle Diagram Construction Working ORStatementDiagramDerivation for EGraph

1211

1121

5

BLUE PRINT

UNIT TOPIC VSA SA I SA II LA TOTAL QP

TOTAL MARKS

1 Electrostatics 1 1 1 3 82 Current Electricity 1 2 3 73 Magnetic effect of

Current and Magnetism

1 2 1 4 8

4 Electromagnetic Induction & Alternating currents

1 2 1 4 8

5 Electromagnetic Waves

1 1 2 3

6 Optics 1 1 2 1 5 147 Dual nature of Matter 1 1 2 48 Atoms and Nuclei 1 1 1 3 69 Electronic Devices 1 1 2 710 Communication

systems1 1 2 5

8 10 9 3 30 70

Calculate current through a capacitor of capacitance 10 F connected as shown in the figure.

10F2

2

2V

1

If the intensity of incident radiation is doubled, how does the stopping potential change?

What is the source of displacement current?

2

3

4

5

6

7

8

9

10

OR Find the force between two infinitely long straight conductor carrying current

in the same direction.

11

12

13

14

15

16

17

18

OR

Explain principle of potentiometer. How it can be used to compare emf’s two primary cells

19

20

21

22

State the condition under which the phenomenon of diffraction of light takes place. Derive an expression for the width of the central maximum due to diffraction of light at a single slit.

The radii of curvature of two surfaces of a biconcave lens are 15cm and 30cm. Find focal length of the lens if refractive index of the lens is 1.5 with respect to air.

Define half – life period of a radioactive material. Half life of a certain radioactive material against α –decay is 138 days. After what lapse of time the undecayed fraction of the material will be 6.25 %.

23

24

25

26

27

ORDerive an expression for fringe width in Young’s double slit experiment What is the effect on the interference fringes in Young’s double slit experiment due toa) The screen is moved away from the plane of the slits.b) Source is replaced by another source of shorter wavelength.c) If the separation between is increasedd) The source slit is moved closer to the double slit planee) The width of the source slit is increased

Explain with the help of a circuit diagram, the working of npn transistor as a common emitter amplifier. What is the phase relation between input and output of the CE amplifier? OR

Explain with the help of a circuit diagram, the working of npn transistor as an oscillator.

OR

KENDRIYA VIDYALAYA RWF, YELAHANKA NEWTOWN BANGALORE MODEL PAPER-4

CLASS XII PHYSICS MARKING SCHEME

28

29

30

OR

11.

12

13

14

15

9

17

18

19

20

21

22

23

24.

25

26

27

28

ORDerivation of expression for fringe width

a. Angular separation of the fringes remains constantb. separation of the fringes decreasesc. separation of the fringes decreasesd. S/D< /d otherwise no pattern is observed.e. if above condition is not satisfied interference pattern disappears.f. increases the brightness of the fringes.g. clear fringes are not observed.

29 Diagram 11/2 Construction (Biasing) 1 Working 11/2

Phase relation 1

30