12th Physics ch#12 MCQs with Key

Chapter 12

1. If the potential difference across the two plates of a parallel plate capacitor is doubled, then the energy stored in it will become
(a) two times (b) four times (c) eight times (d) remains constant

2. Solid bodies are charged due to the transfer of
(a) electrons (b) protons (c) neutrons (d) All of these

3. The SI unit of electric intensity is
(a) V/m (b) tesla (c) N/m (d) C/m

4. If

, then maximum value of flux is obtained if the angle between

and

is
(a)

(b)

(c)

(d)

5. SI unit of electric flux is
(a)

(b)

6. Electric lines of force are parallel an equally spaced, then electric field is
(a) weak (b) strong (c) non-uniform (d) uniform

7. If the distance between two point charges is doubled, the force between them will become
(a) double (b) half (c) three times (d) one fourth

8. The SI unit of “K” in Coulomb’s law is

9. Photocopier and inkjet printer are the application of
(a) Electronics (b) Electricity (c) Magnetism (d) Electrostatics

10. The unit of electric charge is
(a) volt (b) henry (c) coulomb (d) weber

11. Sec/ohm is equal to
(a) farad (b) coulomb (c) joule (d) ampere

12. Millikan and Flecher could determine the charge on oil droplet in
(a) thermal equilibrium (b) electrical equilibrium (c) mechanical equilibrium (d) unstable equilibrium

13. Farad is the unit of
(a) charge (b) current (c) electric flux (d) capacitance

14. A 5 MΩ resistor is connected with a 2 μF capacitor. The time constant of the circuit is
(a) 0.1 s (b) 1 s (c) 2.5 s (d) 10 s

15. The unit of electric field strength is
(a) newton (b) coulomb (c) joule/coulomb (d) newton/coulomb

16. The electric force of repulsion between two electrons at a distance of 1 m is

17. When vector area is held perpendicular to the electric field lines, then the magnitude of electric flux is
(a) maximum (b) minimum (c) either maximum or minimum (d) negative

18. Unit of strength of electric field is
(a) joule/coulomb (b) coulomb/volt (c) volt/meter (d) none of these

19. Under the action of electric field, molecules of a dielectric
(a) begin to vibrate (b) become electric dipole (c) are ionized (d) are charged

20. Electric flux is a
(a) vector with unit

(b) scalar with the unit

(d) scalar with the unit

21.

is the unit of
(a) force (b) charge (c) current (d) electric intensity

22. What does

stands for
(a) electric field (b) electric potential (c) electric flux (d) electric force

23. One of the practical application of electrostatic induction is
(a) laser (b) x-rays machine (c) photocopier (d) Wilson cloud chamber

24. If the magnitude of charges and distance between them is doubled then force will be
(a) doubled (b) halved (c) unaffected (d) one fourth

25. The increase in capacitance of a capacitor due to presence of dielectric is due to
(a) electric polarization (b) electrification (c) ionization (d) electrolysis

26. A particle having 2e charge falls through a potential difference of 5V. Energy acquired by it is
(a) 2.5 eV (b) 20 eV (c) 0.4 eV (d) 10 eV

27. The word “zerography” means
(a) writing by left hand (b) writing by children (c) dry writing (d) writing by water colours

28. The force experienced by unit positive charge placed at a point in electric field is called
(a) Coulomb’s force (b) Faraday’s force (c) Lorantz’s force (d) Electric field intensity

29. When an area is held perpendicular to the field lines, then the magnitude of electric flux is
(a) negative (b) maximum (c) minimum (d) zero

30. One electron volt is equal to

31. An inkjet printer used _________ in its operation.
(a) positrons (b) neutrons (c) an electric charge (d) protons

32. When an insulating medium is placed between two charges, the electrostatic force is
(a) increased (b) zero (c) decreased (d) same

33. The lines which provide information about the electric force exerted on charged particle are
(a) magnetic field lines (b) electric field lines (c) tangent lines (d) curved lines

34. Absolute potential difference due to point charge of 1C at a distance of 1 m is given by

35. Coulomb per volt is called
(a) farad (b) ampere (c) joule (d) ohm

36. 1 joule =

37. How many electrons will have charge of one coulomb

38. Two point charges +2 coulomb and +6 coulomb repel each other if a charge of 2 coulomb is given to each of them the electric force will be
(a) 0N (b)

N (attractive)
(c)

N (repulsive) (d)

N (attractive and repulsive)

39. Unit of energy density of electric field is

40. The term RC has same unit as that of
(a) potential (b) capacitance (c) energy (d) time

41. The amount of energy equal to

J is called
(a) one volt (b) one milli volt (c) one electron volt (d) one mega electron volt

42. Product of resistance and capacitance is called
(a) gas constant (b) resistivity (c) Boltzman constant (d) time constant

43. A positively charged particle of certain mass may be held suspended (at rest) in electric field of suitable strength if the field is directed
(a) outward (b) inward (c) upward (d) downward

44. When an RC circuit is connected across a battery amount of charge deposited on plates is ________ times the equilibrium charge after one time constant
(a) 0.63 (b) 0.67 (c) 0.75 (d) 0.86

45. Two equal and opposite point charges are separated by a distance 2d. The electric potential at the midway between them is
(a) zero (b) high (c) low (d) constant

46. Energy density in case of capacitor is proportional to
(a) ε_o (b) C (c) V² (d) E²

47. When dielectric material is placed in an electric field it
(a) conducts (b) exhibit electric charge (c) undergoes electrolysis (d) becomes polarized

48. The charging time of capacitor depends upon

49. Presence of dielectric always
(a) increases the electrostatic force (b) decreases the electrostatic force
(c) does not affect (d) doubles the electrostatic force

50. The capacitance of a parallel plate capacitor in vacuum is

51. If the potential difference across two plates of a capacitor is doubled, then energy stored in it will be
(a) two times (b) eight times (c) four times (d) remains same

52. When a dielectric is placed between two charges, then Coulomb’s force will be
(a) increased (b) decreased (c) zero (d) negative

53. A capacitor stores energy in the form of
(a) magnetic field (b) heat energy (c) electrical energy (d) mechanical energy

54. Farad is defined as
(a) coulomb/volt (b) ampere/volt (c) coulomb/joule (d) volt/coulomb

55. A charge of 1 μC experiences a force of