Physics class 12 chapter 2 Objective Questions

1. The dimensions of fall of potential per unit distance are given by:

(a) [MLT^-3 A^-1]

(b) [ML²T^-2A^-1]

(c) [ML²T^-2A^-3]

(d) [MLT^-2A^-2]

Answer: (c) [ML²T^-2A^-3]

2. Which of the following is blocked by a capacitor ?

(a) A.C.

(b) D.C.

(c) Both A.C. and D.C.

(d) Neither A.C. nor D. C

Answer: (b) D.C.

3. Two copper spheres of the same radius, one solid and the other hollow, are charged to the same potential. Which will have more charge?

(a) Solid sphere

(b) Hollow sphere

(c) Both will have an equal charge

(d) None of these

Answer: (c) Both will have an equal charge

4. The capacitance of a capacitor will decrease if we introduce a slab of:

(a) copper

(b) aluminium

(c) zinc

(d) None of these

Answer: (d) None of these

5. Two capacitors of capacitance 6 µF and 4 µF are put in series across a 120 V battery. What is the potential difference across the 4 µF capacitor ?

(a) 72 V

(b) 60 V

(c) 48 V

(d) zero

Answer: (a) 72 V

6. In which of the following forms is the energy stored in a capacitor?

(a) Charge

(b) Potential

(c) Capacitance

(d) Electric field

Answer: (d) Electric field

7. Two conducting spheres of radii r₁and r₂ are equally charged. The ratio of their potential is

(a) (r₁/r₂)²

(b) (r₁r₂)²

(c)(r₁/r₂)

(d) (r₂/r₁)

Answer: (b) (r₁r₂)²

8. Twenty seven drops of mercury are charged simultaneously to the same potential of 10 volts. What will be potential if all the charged drops are made to combine to form one large drop ?

(a) 180 V

(b) 90 V

(c) 120 V

(d) 45 V

Answer: (b) 90 V

9. The P.E. of an electric dipole is maximum when it makes an angle θ with electric field. The value of θ is :

(a) π²

(b) π

(c) zero

(d) 3π2

Answer: (b) π

10. The amount of work required to increase the distance between -6µC and 4µC from 6 cm to 18 cm will be :

(a) 1.8 J

(b) 2.4 J

(c) 1.8 µJ

(d) 2.4 µJ

Answer: (b) 2.4 J

11. An electron initially at rest is accelerated through a potential difference of one volt. The energy gained by electron is:

(a) 1 J

(b) 1.6 × 10^-19 J

(c) 10^-19 J

(d) None of these

Answer: (b) 1.6 × 10^-19 J

12. A bird sitting on a high power line:

(a) gets killed instantly

(b) gets a mild shock

(c) gets a fatal shock

(d) is not affected practically

Answer: (d) is not affected practically

13. Choose the SI unit of electric potential energy :

(a) Joule

(b) Coulomb

(c) Netwon per coulomb

(d) Erg

Answer: (a) Joule

14. The capacitance of earth, viewed as a spherical conductor of radius 6408 km is:

(a) 1420 µF

(b) 712 µF

(c) 680 µF

(d) 540 µF

Answer: (b) 712 µF

15. A capacitor is connected to a cell of emf E having some internal resistance r, the potential across the:

(a) cell is < E

(b) cell is E

(b) cell is > E

(d) capacitor is E

Answer: (b) cell is E

16. If a +ve charge is moved from low to high potential region,
    the electric potential energy:

(a) decreases

(b) increases

(c) remain the same

(d) may increase or decrease

Answer: (b) increases

17. A capacitor is connected across a battery and the plate separation of capacitor is increased without removing the battery, then:

(a) capacitance will increase

(b) charge stored will increase

(c) energy stored will decrease

(d) potential difference will increase

Answer: (c) energy stored will decrease

18. Two capacitors of 3 µF and 6 µF are connected in series with a battery of P.d. 12 V. The P.d. across 3µF and 6µF
    capacitors respectively will be :

(a) 8 V, 4 V

(b) 6 V, 6 V

(c) 4 V, 8 V

(d) 9 V, 3 V

Answer: (a) 8 V, 4 V

19. An electric charge of 425 f µC is removed from a fully charged capacitor of capacitance 8.5µF. Its potential will be lowered by:

(a) 75 V

(b) 100 V

(c) 85 V

(d) 50 V

Answer: (b) 100 V

20. A dielectric is placed in between the two parallel plates of a capacitor as shown in the figure. The dielectric constant of the dielectric being K. If the initial capacity is C, then the new capacity will be:

(a) (K + l).C

(b) K.C

(c) (K+1)2 C

(d) (k – l) C

Answer: (c) (K+1)2 C

21. Minimum number of capacitor of 2µF each required to obtain a capacitance of 5µF will be:

(a) 4

(b) 3

(c) 5

(d) 6

Answer: (a) 4

22. When a dielectric slab is introduced between the plates of a parallel plate capacitor which remains connected to a battery then charge on the plates relative to earlier charge is :

(a) more

(b) less

(c) less or may be more

(d) same

Answer: (a) more

23. Choose the vector physical quantity:

(a) Electric flux

(b) Electric potential

(c) Electric potential energy

(d) Electric intensity

Answer: (d) Electric intensity

24. The surface density of charge is measure:

(a) Cm^-1

(b) Cm^-2

(c) Cm^-3

(d) JC^-1

Answer: (b) Cm^-2

25. A polythene piece rubbed with wool is found to have a negative charge of 6.4 × 10^-9 How many electrons have been transferred during the process?

(a) 4 × 10¹²

(b) 4 × 10¹¹

(c) 4 × 10¹⁰

(d) None of these

Answer: (c) 4 × 10¹⁰

26. In the above question:

(a) no electrons are transferred

(b) electrons are transferred from wool to x polythene

(c) electrons are transferred from polythene to wool

(d) nothing can be decided

Answer: (b) electrons are transferred from wool to x polythene

27. In previous question, mass transferred to polythene is:

(a) 3.64 × 10²⁰ kg

(b) 4 × 10^-28 kg

(c) 4 × 10¹⁰ kg

(d) None of these

Answer: (a) 3.64 × 10²⁰ kg

28. What is the number of electrons in 100 g water?

(a) 3.35 × 10²⁴

(b) 3.35 × 10²⁵

(c) 6.02 × 10²³

(d) None of these

Answer: (a) 3.35 × 10²⁴

29. A uniform electric field of 10 NC^-1exists in the vertically downward direction. What is the increase in the electric potential asonegoes up through a height of 300 cm ?

(a) 15 V

(b) 30 V

(c) 45V

(d) None of these

Answer: (b) 30 V

30. The electric potential of earth is taken as:

(a) zero

(b) infinity

(c) unity

(d) None of these

Answer: (a) zero