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Success Group of Institutions SOUTH GATE, MADURAI-1.

PHYSICS Quarterly Examination – 2014 Time: 3hr

Total marks - 150

Std: XII

Part – A I) Choose the correct answer: 30 X 1 = 30 1) The electrostatic force between two point charges kept at a distance d apart, in a medium εr = 6, is 0.3 N. The force between them at the same separation in vacuum is. a) 20 N b) 0.5 N c) 1.8 N d) 2 N 2) Two point charges +4q and +q are placed 30 cm apart. At what point on the line joining them the electric field is zero? a) 15 cm from the charge q b) 7.5 cm from the charge q c) 20 cm from the charge 4q d) 5 cm from the charge q 3) Which of the following quantities is a scalar? a) electric force b) electric field c) dipole moment d) electric potential 4) What is the use of the Van de Graff generator? a) To produce very high voltage b) To produce high current c) To produce high electric field strength d) To produce high electric power 5) Capacity of the conductor depends on. a) the dimension of a conductor b) the charge c) the medium d) the dimension of a conductor and the medium 6) A charge of 60 C passes through an electric lamp in 2 minutes. Then the current in the lamp is. a) 30 A b) 1 A c) 0.5 A d) 5 A 7) The current flowing in a conductor is proportional to. a) drift velocity b) 1/ area of cross section c) 1/no of electrons d) square of area of cross section 8) If the resistance of a coil is 2 Ω at 00 C and α = 0.004 /0 C, then its resistance at 1000 C is. a) 1.4 Ω b) 0 Ω c) 4 Ω d) 2.8 Ω 9) The brown ring at one end of a carbon resistor indicates a tolerance of______ a) 1% b) 2 % c) 5% d) 10 % 10) The unit of conductivity is. a) mho b) ohm c) ohm-m d) mho-m-1 11) The period of revolution of a charged particle inside a cyclotron does not depend on a) the magnetic induction b) the charge of the particle c) the velocity of the particle d) the mass of the particle 12) The torque on a rectangular coil placed in a uniform magnetic field is large, when a) the number of turns is large b) the number of turns is less c) the plane of the coil is perpendicular to the field d) the area of the coil is small

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13) A galvanometer of resistance G Ω is shunted with S Ω .The effective resistance of the combination is R. Then, which of the following statements is true? a) G is less than S b) S is less than R but greater than G c) Rα is less than both G and S d) S is less than both G and Rα 14) Which of the following produces large joule heating effect? a) 1 A current through 2Ω resistor for 3 second b) 1 A current through 3Ω resistor for 2 second c) 2 A current through 1Ω resistor for 2 second d) 3 A current through 2Ω resistor for 1 second 15) Peltier coefficient at a junction of a thermocouple depends on the. a) current in the thermocouple b) time for which current flows c) temperature of the junction d) charge that passes through the thermo couple 16) A DC of 5A produces the same heating effect as an AC of a) 50 A rms current b) 5 A peak current c) 5A rms current d) none of these π π 17) In an AC circuit the applied emf e = E0 sin (ωt + ) leads the current I = I0 sin (ωt – ) by a)

𝜋

b)

2

2

𝜋

c) π

4

2

d) 0

18) In an a.c. circuit with an inductor a) voltage lags current by π/2 b) voltage and current are in phase c) voltage leads current by π d) current lags voltage by π/2 19) The unit henry can also be written as. a) V As-1 b) Wb-1 A c) Ω s d) all 20) The Q-factor of an a.c. circuit containing a resistance R, inductance L and capacitor C is. a) Q =

1 𝐿𝐶

b) Q =

1

𝐶

𝑅

𝐿

c) Q =

1

𝐿

𝑅

𝐶

d) Q =

1 𝐿𝑅

21) Refractive index of glass is 1.5. Time taken for light to pass through a glass plate of thickness 10 cm is. a) 2 × 10-8 s b) 2 × 10-10 s c) 5 × 10-8 s d) 5 × 10-10 s 22) A beam of monochromatic light enters from vacuum into a medium of refractive index µ. The ratio of the wavelengths of the incident and refracted waves is. a) µ : 1 b) 1 : µ c) µ2 : 1 d) 1 : µ2 23) The path difference between two monochromatic light waves of wavelength 4000 Å is 2 × 10-7 m. The phase difference between them is. a) π b) 2 π c) 3 π d) π /2 24) In an electromagnetic wave ________ (a) power is equally transferred along the electric and magnetic fields (b) power is transmitted in a direction perpendicular to both the fields (c) power is transmitted along electric field (d) power is transmitted along magnetic field 25) In the grating formula sin θ = Nmλ, the unit of N is ________ a) meter b) meter-1 c) no unit d) (meter)2

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26) Energy levels A, B, C of a certain atom correspond to increasing values of energy (i.e.,) E A < EB < EC. If λ1, λ2, λ3 are the wavelengths of radiations corresponding to the transitions C to B, B to A and C to A respectively, which of the following statements is correct. a) λ3 = λ1 + λ2

b) λ3 =

𝜆1 𝜆2 𝜆 1 +𝜆 2

d) 𝜆23 = 𝜆12 + 𝜆22

c) λ1 = λ2 + λ3 = 0

27) The elliptical orbits of electron in the atom were proposed by. a) J. J. Thomson b) Bohr c) Sommerfeld d) de Broglie 28) The energy of a photon of characteristic X-ray from a Coolidge tube comes from (a) the kinetic energy of the free electrons of the target (b) the kinetic energy of ions of the target (c) the kinetic energy of the striking electron (d) an atomic transition in the target. 29) If a and b are semi-major and semi-minor axes of the ellipse respectively and l is the orbital quantum number, then the expression to find the possible elliptical orbits is. 𝑏

𝑙+1

𝑎

𝑛

a) =

𝑏

𝑙−1

𝑎

𝑛

b) =

𝑎

𝑙+1

𝑏

𝑛

c) =

𝑎

𝑙−1

𝑏

𝑛

d) =

30) X−ray is. a) phenomenon of conversion of kinetic energy into radiation b) conversion of momentum c) conversion of energy into mass d) principle of conservation of charge Part – B II) Answer any fifteen of the following questions: 15 x 3 = 45 31. What are non polar molecules? Give some examples. 32. Why is it safer to be inside a car than standing under a tree during lightning? 33. State Gauss law. 34. How much time 1020 electrons will take to flow through a point, so that the current is 200 mA? 35. Define drift velocity and mobility. 36. The resistance of a field coil measures 50 Ω at 20 0 C and 65 Ω at 700 C. Find the temperature coefficient of resistance. 37. Define temperature coefficient of the resistance. 38. Define peltier coefficient. 39. State right hand palm rule. 40. In a tangent galvanometer, a current of 1 A produces a deflection of 300. Find the current required to produce a deflection of 600. 41. Mention the methods of produced induced emf. 42. An air craft having a wingspan of 20.48 m flies due north at a speed of 40 ms -1. If the vertical component of earth’s magnetic field at the place is 2 x 10-5 T. Calculate the emf induced between the ends of the wings. 43. Define inductive reactance. 44. Distinguish between interference and diffraction. 45. Define polarizer and analyser. 46. Define specific rotation.

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47. Distinguish between soft and hard X – rays. 48. Calculate the longest wavelength that can be analysed by a rock salt crystal of spacing d = 2.82Å in the first order. 49. Write any three properties of cathode rays. 50. Find the minimum wavelength of X−rays produced by an X−ray tube at 1000 kV. Part – C III) Question no. 56 is compulsory; Answer any six of the remaining 7 x 5 = 35 51. A parallel plate capacitor with air between the plates has a capacitance of 8 pf. What will be the capacitance, If the distance between the plates be reduced to half and the space between them is filled with a substance of dielectric constant 6. 52. Give the properties of electric lines of force. 53. Determination of internal resistance of a cell using voltmeter. 54. Explain the action of Daniel cell. 55. Explain how will you convert galvanometer in an ammeter? 56. a) A moving ciol galvanometer of resistance 20 Ω produces full scale deflection for a current of 50 mA. How you will convert the galvanometer into (i) an ammeter of range 20 A and (ii) a voltmeter of range 120 V. [Or] b) A soap film of refractive index 1.33 is illuminated by white light incident at an angle 300. The reflected light is examined by spectroscope in which dark band corresponding to the wavelength 6000 A0 is found. Calculate the smallest thickness of the film. 57. Give some energy losses in transformer. 58. Derive an expression for emf induced by changing area enclosed by the coil. 59. Give the uses of polaroids 60. State and explain Brewster’s law. 61. Prove that the energy of an electron for hydrogen atom in nth orbit is En =

−𝑚 𝑒 4 8𝜀 02 𝑛 2 ℎ 2

.

62. Give the shortcomings of Bohr’s theory. Part – D IV) Answer any four of the following: 4 x 10 = 40 63. State gauss law. Derive an expression for electric field due to the infinite long straight charged wire. 64. Derive an expression for electric potential due to an electric dipole at a point. Give also special cases for this case. 65. Derive an expression for magnetic induction due to a current carrying circular coil. 66. Explain construction and working of AC generator.

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67. A source of alternating emf is connected to a series combination of a resistor R an inductor L and a capacitor C. Obtain with the help of a vector diagram and impedance diagram, an expression for (i) the effective voltage (ii) the impedance (iii) the phase relationship between the current and the voltage. 68. Explain about Raman effect. 69. Explain the working of Ruby laser with neat sketch. 70. Describe the J. J. Thomson method for determining the specific charge of an electron.

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