Physics Questions and Answers – Electrostatic Potential

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This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Electrostatic Potential”.

1. Work done to bring a unit positive charge from infinity to a point in an electric field is known as _______
a) Electric potential
b) Electric field intensity
c) Electric dipole moment
d) The total energy of the point charge

Explanation: Electric potential is defined as the amount of work done to bring a unit positive charge from an infinite distance to a particular point of an electric field. The total energy of that point charge means the sum of kinetic energy and potential energy which is not the same as the potential energy if the particle is in motion.

2. If VA and VVB are the potentials of the two points A and B, what will be the correct relation between the electric field and the potential difference between the points? The distance between the points is d.

a) VA-VB=Ed
b) VB-VA=Ed
c) VA-VB=$$\frac {E}{d}$$
d) VA-VB=$$\frac {d}{E}$$

Explanation: The direction of the electric field is always from a point with a higher potential to a point of lower potential. According to the diagram VA > VB. Therefore, to bring a positive point charge from B to A, work done=-Ed which will be equal to the potential difference between the points i.e. VA-VB=-Ed.

3. What is the dimension of electric potential?
a) [M L T-2]
b) [M L T-3 I]
c) [M L T-3 I-1]
d) [M L2 T-3 I]

Explanation: Potential can be simply defined as work done on a unit charge, therefore the dimension=$$\frac {the \, dimension \, of \, work}{the \, dimension \, of \, charge}=\frac {[M L T^{-2}]}{[I T]}$$=[M L T-3 I-1]. The dimension of potential energy in mechanics is not the same as electric potential energy though both of them are the unit of energy. In mechanics, it is defined as work done on a unit mass.
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4. Electric potential varies with distance such that V(x) =ax-bx3; where a and b are constants. Where will the electric field intensity be zero?
a) x=$$\frac {a}{b}$$
b) x=$$\frac {a}{3b}$$
c) x=$$\sqrt{\frac {a}{b}}$$
d) x=+$$\sqrt{\frac {a}{3b}}$$ and x=-$$\sqrt{\frac {a}{3b}}$$

Explanation: We know that E=-$$\frac {dv}{dx}$$
∴ E = –$$\frac {d}{dx}$$ (ax – bx3) = -(a – 3bx2)
Electric field will be zero. ∴ E = 0 ⇒ (a-3bx2) = 0
⇒ a = 3bx2
⇒ x2 = $$\frac {a}{3b}$$ = x = ±$$\sqrt{\frac {a}{3b}}$$

5. 1 electron volt= __________ J.
a) 1.6*10-19
b) 4.8*10-19
c) 1.6*10-10
d) 10

Explanation: 1 electron volt is the amount of work done if an electron is passed through a potential difference of 1V. Therefore the work done = 1V*charge of an electron = 1.602*10-19 J. But it is a small quantity and hence we use kilo electron volt and mega electron volt in practical.
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6. 1 V/m= _______
a) 1N/C
b) 3*1010 N/C
c) 107 N/C
d) 1010 N/C

Explanation: From the definition, we know that electric field E=$$\frac {-dv}{dx}$$. Therefore V/m is the unit of electric field intensity. 1 V/m means the amount of electric field in which if we move a unit positive charge by 1 m, the work done will be 1N. Therefore, the electric field will be 1N/C.

7. The electric potential difference between two points is a path function. The statement is __________
a) True
b) False

Explanation: Electric potential depends only on the electric field intensity and the amount of charge. It has no dependency on the path by which the charge is traveling. Therefore, if we move a charge from one point to another in presence of an electric field in a straight line or a curve line, work done in both the cases will be the same i.e. potential difference between the points will be the same.

8. By performing a set of experiments, a scientist found that the electric field between two points A and B is zero. What can he conclude regarding the potential of the two points?
a) VA=0, VB=0
b) VA>VB
c) VA+VB
d) VA=VB

Explanation: We know thatVAB=VA-VB=-$$\int_A^B$$E.dx. But E=0, so the value of the integral becomes zero. Therefore VA=VB is obtained. The electric field is always directed from a point of higher potential to a point of lower potential. But if the potential of two points is the same, i.e. no potential difference, then there will be no electric field.

9. Earth’s potential is _______
a) Zero
b) Highly positive
c) Highly negative
d) Varies from place to place

Explanation: We consider earth as the storage of infinite positive as well as a negative charge. Therefore, the potential of the earth is always considered to be zero and the potential of every body is measured with respect to earth. That’s why if we connect any charged body to the earth, its potential instantaneously becomes zero.

10. If a charged body is moved in an electric field against the Coulomb force, then ________
a) Work is done on the body by an external agent
b) Work is done by the electric field
c) Electric field intensity decreases
d) The total energy of the system decreases

Explanation: To move a body against some force, work is to be done on the body. In this case, an external force is to be applied on the body to move it i.e. an external work is to be done. As we are moving the body against the Coulomb’s force, hence no work is done on the body by the electric field.

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