Electrostatic Potential and Capacitance

Electrostatic Potential and Capacitance Class 12 Physics MCQs

1. Which of the following statement is true?
(a) Electrostatic force is a conservative force.
(b) Potential at a point is the work done per unit charge in bringing a charge from any point to infinity.
(c) Electrostatic force is non-conservative
(d) Potential is the productof charge and work.

2. 1 volt is equivalent to

3. The work done in bringing a unit positive charge from infinite distance to a point at distance x from a positive charge Q is W. Then the potential at that point is

4. Consider a uniform electric field in the z-direction. The potential is a constant
(a) for any x for a given z
(b) for any y for a given z
(c) on the x-y plane for a given z
(d) all of these

5. Equipotential surfaces
(a) are closer in regions of large electric fields compared to regions of lower electric fields.
(b) will be more crowded near sharp edges of a conductor.
(c) will always be equally spaced.
(d) both (a) and (b) are correct.

6. In a region of constant potential
(a) the electric field is uniform.
(b) the electric field is zero.
(c) there can be no charge inside the region.
(d) both (b) and (c) are correct.

7. A test charge is moved from lower potential point to a higher potential point. The potential energy of test charge will
(a) remain the same
(b) increase
(c) decrease
(d) become zero

8. An electric dipole of moment \(\vec{p}\) is placed in a uniform electric field \(\vec{E}\) . Then
(i) the torque on the dipole is \(\vec{p} \times \overrightarrow{\mathrm{E}}\)
(ii) the potential energy of the system is \(\vec{p} . \overrightarrow{\mathrm{E}}\)
(iii) the resultant force on the dipole is zero. Choose the correct option.
(a) (i), (ii) and (iii) are correct
(b) (i) and (iii) are correct and (ii) is wrong
(c) only (i) is correct
(d) (i) and (ii) are correct and (iii) is wrong

9. If a conductor has a potential V ≠ 0 and there are no charges anywhere else outside, then
(a) there must be charges on the surface or in¬side itself.
(b) there cannot be any charge in the body of the conductor.
(c) there must be charges only on the surface.
(d) both (a) and (b) are correct.

10. Which of the following statements is false for a perfect conductor?
(a) The surface of the conductor is an equipoten-tial surface.
(b) The electric field just outside the surface of a conductor is perpendicular to the surface.
(c) The charge carried by a conductor is always uniformly distributed over the surface of the conductor.
(d) None of these.

11. Dielectric constant for a metal is
(a) zero
(b) infinite
(c) 1
(d) 10

12. When air is replaced by a dielectric medium of constant K, the maximum force of attraction between two charges separated by a distance
(a) increases K times
(b) remains unchanged
(c) decreases K times
(d) increases K^-1 times

13. In a parallel plate capacitor, the capacity increases if
(a) area of the plate is decreased.
(b) distance between the plates increases.
(c) area of the plate is increased.
(d) dielectric constantly decreases.

14. A parallel plate air capacitor is charged to a potential difference of V volts. After disconnecting the charging battery the distance between the plates of the capacitor is increased using an insulating handle. As a result the potential difference between the plates
(a) increases
(b) decreases
(c) does not change
(d) becomes zero

15. Two identical capacitors are joined in parallel, charged to a potential V, separated and then connected in series, the positive plate of one is connected to the negative of the other. Which of the following is true?
(a) The charges on the free plated connected to-gether are destroyed.
(b) The energy stored in ths system increases.
(c) The potential difference between the free plates is 2V.
(d) The potential difference remains constant.

16. A capacitor has some dielectric between its plates, and the capacitor is connected to a dc source. The battery is now disconnected and then the dielectric is removed, then
(a) capacitance will increase.
(b) energy stored will decrease.
(c) electric field will increase.
(d) voltage will decrease.

17. Two spherical conductors each of capacity C are charged to potential V and -V. These are then connected by means of a fine wire. The loss of energy is
(a) zero
(b) \(\frac{1}{2}\)CV²
(c) CV²
(d) 2 CV²

Question 18.
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]

Question 19.
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

Question 20.
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

Question 21.
The capacitance of a capacitor will decrease if we introduce a slab of:
(a) copper
(b) aluminium
(c) zinc
(d) None of these

Question 22.
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

Question 23.
In which of the following forms is the energy stored in a capacitor?
(a) Charge
(b) Potential
(c) Capacitance
(d) Electric field

Question 24.
Two conducting spheres of radii r₁ and r₂ are equally charged. The ratio of their potential is
(a) (r₁/r₂)²
(b) (r₁r₂)²
(c)(r₁/r₂)
(d) (r₂/r₁)

Question 25.
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

Question 26.
The P.E. of an electric dipole is maximum when it makes an angle θ with electric field. The value of θ is :
(a) \(\frac{π}{2}\)
(b) π
(c) zero
(d) \(\frac{3π}{2}\)

Question 27.
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

Question 28.
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

Question 29.
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

Question 30.
Choose the SI unit of electric potential energy :
(a) Joule
(b) Coulomb
(c) Netwon per coulomb
(d) Erg

Question 31.
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

Question 32.
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

Question 33.
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

Question 34.
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

Question 35.
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

Question 36.
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

Question 37.
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) \(\frac{(K+1)}{2}\) C
(d) (k – l) C

Question 38.
Minimum number of capacitor of 2µF each required to obtain a capacitance of 5µF will be:
(a) 4
(b) 3
(c) 5
(d) 6

Question 39.
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

Ans. (a)
Question 23.
Choose the vector physical quantity:
(a) Electric flux
(b) Electric potential
(c) Electric potential energy
(d) Electric intensity

Question 40.
The surface density of charge is measure:
(a) Cm^-1
(b) Cm^-2
(c) Cm^-3
(d) JC^-1

Question 41.
A polythene piece rubbed with wool is found to have a negative charge of 6.4 × 10^-9c. How many electrons have been transferred during the process?
(a) 4 × 10¹²
(b) 4 × 10¹¹
(c) 4 × 10¹⁰
(d) None of these

Question 42.
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

Question 43.
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

Question 44.
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

Question 45.
A uniform electric field of 10 NC^-1 exists 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

Question 46.
The electric potential of earth is taken as:
(a) zero
(b) infinity
(c) unity
(d) None of these