CLASS 12 PHYSICS ONE MARK QUESTIONS WITH ANSWERS

ONE MARK QUESTIONS WITH ANSWERS 

Hi students, I have made my best effort in this short time to post the Q&A given below.  The main aim is to help students answer one mark and also other conceptual questions with these points in mind. Kindly go through this after completely learning all chapters.  

Note:  Students are advised to read all the chapters thoroughly and take points then and there.  

Also note that the answers are marked in blue.

 

1. Coulombian force is a central and electric force.

2. An infinite number of capacitors  with capacitances 1 μF, 1/2 μF, 1/4 μF , 1/8 μF.. etc are connected in parallel combination.  Their equivalent capacitance will be 2 μF.

3. The power of electric circuit is V²/R.

4. The radius of a circular path in which an electron will move, when subjected to a perpendicular uniform magnetic field B is mv/Be

5. Infrared radiation causes heating effect in sunlight.

6. Final image in astronomical telescope is virtual and inverted

7. Current is increased in a step down transformer.

8. Magnetic  lines of force are always closed

9. The magnetic flux through a circuit of resistance R changes by an amount ΔØ in a time ∆t.  The total electric charge Q that  passes any point in the circuit during the time  ∆t  is represented by Q=ΔØ/R

10. Alternating current cannot be measured by DC ammeter because average value of current for a complete cycle is zero

11. The kinetic energy of an electron which is accelerated in the potential difference of 100 V is 1.6 x 10 ⁻¹⁷ J

12. With the increase in temperature, width of the forbidden gap decreases.

13. In nuclear fission, the percentage of mass converted into energy is about 0.1%

14. The n-type semiconductors are obtained when germanium is doped with arsenic or phosphorous.

15. A current of 10 ampere flows in a wire for 10 seconds.  If the potential difference across the wire is 15 volt, the work done will be 1500 J

16. Two point charges Q and -2Q are placed at some distance apart.  If the electric field at the location of Q is E, then the electric field at the location of -2Q will be -E/2

17. The electric potential due to a small electric dipole at a large distance r from the centre of the dipole is proportional to 1/r²

18. If a current of 300 mA is flowing in a conductor, then the number of electrons passed through the conductor in 4 minutes is 4.5 x 10²⁰

19. Two thin long parallel wires separated by a distance d carry a current of i ampere in the same direction.  They will attract each other with a force of μ₀i²/(2πd)

20. Two long straight parallel conductors separated by a distance of 0.5 m carry currents of 5 A and 8 A in the same direction. The force per unit length experienced by each other is 1.6 x 10⁻⁵ N (attractive)

21. The direction of null points are on the equatorial line of a bar magnet, when the north pole of the magnet is pointing towards north.

22.If a wire of length 2 m is moving with a velocity of 1m/s perpendicular to a magnetic field of 0.5 T, the EMF induced in the wire will be 1 V

23. When a compact disc is illuminated by a source of white light, coloured lines are observed.  This is due to diffraction.

24. The total energy of an electron in the first excited state of hydrogen atom is about -3.4 eV.  Its KE in this state is 3.4 eV

25. An energy source will supply a constant current into a load, if its internal resistance is zero.

26. Electric intensity due to an electric dipole varies with distance r as E ∝ rⁿ, where n is equal to -2

27. If a copper plate of thickness b is inserted a parallel plate capacitor, then its new capacitance will be (where d is the distance between plates)  ε₀A/(2d-b)

28. If voltage across a lamp increases by 2 % then increase in its power will be 4 %

29. A diamagnetic material in a magnetic field moves from stronger to weaker parts

30. A charged particle is released from rest in a region of steady and uniform electric and magnetic fields, which are parallel to each other.  The particle will move in a straight line

31. A 2 m solenoid with radius 2 cm and 2000 turns has another solenoid of 1000 turns wound closely near its midpoint. The mutual inductance of solenoids is 1.5 mH

32. The waves which cannot travel in vacuum  are infrasonic waves

33. If light waves emitted by two coherent sources have wavelengths λ₁ and λ₂, then λ₁ = λ₂

 

34. The energy of a photon of wavelength λ is hc/λ

35. The ground state energy of hydrogen atom is -13.6 eV.  The potential energy of the electron in this state is  - 27.2 eV

36. The number of neutrons in an atom of ₉₀Th²³⁰ is 140

37. The electric field required to keep a water drop of mass m just to remain suspended, when charged with one electron, is mg/e

38. A large magnet is broken into two pieces so that their lengths are in the ratio 2:1.  The pole strengths of the two pieces will be in the ratio 1:1

39. The electric field at a point near an infinite thin sheet of charged conductor is σ/2ε₀

40. A 100 W, 200 V bulb is connected to a 160 volt supply. The actual power consumption would be 64 W

41. When a charged particle moves perpendicular to a magnetic field, then speed of the particle remains unchanged.

42. Copper is an example for diamagnetic substance.

43. A parallel plate capacitor with oil between the plates (dielectric constant of oil K=2) has a capacitance C.  If the oil is removed, then capacitance of the capacitor becomes C/2

44. Huygen's wave theory of light could not explain photoelectric  effect

45. If red and violet light rays are of focal length f₁ and f₂, then their wavelength will be λ₁  <  λ₂

46. The specific resistance of a conductor increases with increase of temperature.

47. Gamma rays have maximum penetrating power.

48. Balmer series lies in the visible region of hydrogen spectrum

49. The capacitance of a parallel plate capacitor increases with the introduction of a dielectric between the plates of a capacitor.

50. SI unit of pole strength is Am

51. If a ray of light is incident on a plane mirror at an angle of 30°, then deviation produced by the plane mirror is 120°

52. The elements with same atomic mass,  but different atomic number are isobars.

53. When exposed to sunlight, thin films of oil on water often exhibit brilliant colours due to the phenomenon of  interference.

54. The algebraic sum of all currents meeting at a point in an electrical circuit is zero.

55. Electrical conductivity of semiconductors increases with the rise in temperature.

56. When a body is connected to the earth then electrons from the earth flow into the body.  It means that the body is positively charged.

57 The net charge on a current carrying conductor is zero.

58. If the uniform electric field exists along X-axis then equipotential is along YZ-plane.

59. Lenz's law is associated with principle of conservation of energy.

60. A bar magnet of magnetic moment M is cut into two parts of equal length.  The magnetic moment of either part is M/2

61. The value of peak AC in a 220 V mains is 220√2 V

62. The direction of transmission of electromagnetic wave is parallel to E x B

63. The radius of curvature of plane mirror is infinite.

64. If momentum of a particle is doubled, then its de-Broglie's wavelength will be half.

65. Minimum number of capacitors of 2 μF each required to obtain a capacitance of 5 μF will be 4

66. Rutherford's alpha particle experiment showed that the atoms have nucleus

67. The work done to move a charge along an equipotential from A to B is zero.                               

68. A hollow metal surface of radius 5cm is charged so that the potential on its surface is 10 V.  The potential at the centre of the sphere is 10 V

 

69. A current of 0.8 A flows in a conductor of 40 ohms for 1 minute.  The heat produced in the conductor will be 1536 J

70. An electric heater rated 220 V and 550 W is connected to AC mains.  The current drawn by it is 2.5 A

71. A cell of emf E and internal resistance r is connected in series with an external resistance nr, then the ratio of the terminal potential difference to emf is n/(n+1)

 72. The relative permeability of a substance X is slightly less than unity and that of substance Y is slightly more than unity, then X is diamagnetic and Y is ferromagnetic

73. An ammeter of resistance 0.81 ohms reads upto 1 A.  The value of the required shunt to increase the range to 10 A is 0.09 ohms

74. There is a thin conducting wire carrying current. 

The value of magnetic field induction at any point on the conductor will be zero.

75. In a uniform magnetic field, an electron enters perpendicular to the field.  The path of the electron will be circular.

Note:  Students are advised to do the sums and reasoning themselves based on the concepts they have learnt. If any clarifications needed as regard to the answers, kindly get it verified with your prescribed textbook.

ALL THE BEST FOR YOUR EXAMS