# Physics class 12 chapter 1 Objective Questions

## Electric Charges and Fields Objective

1. Which one of the following is the unit of electric field?

(a) Coulomb

(b) Newton

(c) Volt

(d) N/C

1. Three charges + 3q + q and Q are placed on a st. line with equal separation. In order to maket the net force on q to be zero, the value of Q will be :

(a) +3q

(b) +2q

(c) -3q

(d) -4q

1. If an electric dipole is kept in a uniform electric field then resultant electric force on it is :

(a) always zero

(b) never zero

(c) depend upon capacity of dipole

(d) None

Answer: (a) always zero

1. The number of electron-taken out from a body to produce 1 coulomb of charge will be :

(a) 6.25 × 1018

(b) 625 × 1018

(c) 6.023 × 1023

(d) None

Answer: (a) 6.25 × 1018

1. The work done in rotating an electric dipole in an electric field:

(a) W = ME (1 – cos θ)

(b) W = ME tan θ

(c)W = ME sec θ

(d) None

Answer: (a) W = ME (1 – cos θ)

1. If sphere of bad conductor is given charge then it is distributed on:

(a) surface

(b) inside the surface

(c) only inside the surface

(d) None

1. Electric field in a cavity of metal:

(a) depends upon the surroundings

(b) depends upon the size of cavity

(c) is always zero

(d) is not necessarily zero

Answer: (d) is not necessarily zero

1. The dielectric constant of a metal is:

(a) 0

(b) 1

(c) ∞

(d) -1

1. 1 coulomb is equal to:

(a) 3 × 109 e.s.u.

(b) 13 × 109 e.s.u.

(c) 3 × 1010 e.s.u.

(d) 13 × 1010 e.s.u.

Answer: (a) 3 × 109 e.s.u.

1. Each of the two point charges are doubled and their distance is halved. Force of interaction becomes p times, w here p is :

(a) 1

(b) 4

(c) 1/16

(d) 16

1. Coulomb’s law in vector form can be written as
F⃗= (1/4πεn) (q1q2/r2)r⃗
where ε0 is the permitivity of free space. The SI units of ε0 will be:

(a) N-1m-2C-2

(b) Nm-2C2

(c) N-1m-2C9

(d) Nm-2C2

1. The dimensional representation of cu will be :

(a) [MLT4 A2]

(b) [M-1L-3T4A2]

(c)[ML-2T ]

(d) None of these

1. When placed in a uniform field, a dipole experiences:

(a) a net force

(b) a torque

(c) both a net force and torque

(d) neither a net force nor a torque

Answer: (b) a torque

1. A parrot comes and sits on a bare high power line. It will:

(a) experience a mild shock ‘

(b) experience a strong shock.

(c) get killed instantaneously

(d) not be affected practically

Answer: (d) not be affected practically

1. The SI units of electric dipole moment are:

(a) C

(b) Cm-1

(c) Cm

(d) Nm-1

1. If two conducting sphere are connected after charging separately then:

(a) Electrostatic energy sphere energy will remain conserved

(b) Electrostatic energy charges remains conserved

(c) Electrostatic energy energy and charge remains conserved

(d) None

Answer: (b) Electrostatic energy charges remains conserved

1. A soap bubble is given a negative charge, then its radius:

(a) increases

(b) decreases

(c) remains unchanged

(d) may increase or decrease

1. In non-uniform electric field, electric dipole experiences:

(a) torque only

(b) torque as well as net force

(c) force only

(d) None of these

Answer: (b) torque as well as net force

1. An electron is sent in an electric field of magnitude 9.1 × 106NC-1. The acceleration produced in it is :

(a) 1.6 ms-2

(b) 1.6 × 1018ms-2

(c) 3.2 × 1018ms-2

(d) 0.8 × 1018 ms-2

Answer: (b) 1.6 × 1018ms-2

1. A semicircular arc of radius r is charged uniformly and the charge per unit length is λ. The electric field at the centre is:

(a) λ/2λε0r2

(b) λ/4πε0r

(c) λ2/2πε0r

(d) λ/2πε0r

1. Two point charges +8q and -2q are located at ,v = O and ,v = L respectively. The location of a point on the .v-axis at which the net electric field due to these two point charges b is zero :

(a) 4L

(b) 8L

(c) L/4

(d) 2L

1. The graph drawn between V are r for a non-conducting charged solid sphere of radius R for r < R will be :

(a) straight line

(b) parabola

(c) hyperbola

(d) None of these

Answer: (d) None of these

1. Corona discharge takes place:

(a) at the surface of a conductor

(b) near the sharp points of a conductor

(c) outside the conductor

(d) at the centre of the conductor

Answer: (b) near the sharp points of a conductor

1. The belt of a Vande Graaf generator gets charge by :

(a) corona discharge

(b) induction

(c) electrification

(d) None of these

Answer: (a) corona discharge

1. Quantisation of charge implies:

(a) Charge does not exist

(b) Charge exists on particles

(c) There is a minimum permissible magnitude of charge

(d) Charge can’t be created

Answer: (c) There is a minimum permissible magnitude of charge

1. The conservation of electric charge implies that:

(a) Charge can’t be created

(b) Charge can’t be destroyed

(c) The number of charged particle in the universe is constant

(d) Simultaneous creation of equal and opposite charges is permissible

Answer: (d) Simultaneous creation of equal and opposite charges is permissible

1. The number of electrons contained in one coulomb of charge is:

(a) 6.25 × 1018

(b) 6.25 × 1017

(c) 6.25 × 1019

(d) 1.6 × 1019

Answer: (a) 6.25 × 1018

1. The unit of intensity of electric field is :

(a) metre/volt

(b) Joule/newton

(c) Coulomb/newton

(d) Newton/coulomb

1. 1 V equals to:

(a) 1 J

(b) 1 JC-1

(c) 1 CJ-1

(d) 1 JC

Answer: (b) 1 JC-1

1. 1 V m-1equals to:

(a) 1 N

(b) 1 Mm-1

(c) 1 NC-1

(d) 1 J-1

Answer: (c) 1 NC-1

1. The minimum amount of charge observed so far is:

(a) 1 C

(b) 4.8 × 1-13 C

(c) 1.6 × 10-19 C

(d) 1.6 × 1019 C

Answer: (c) 1.6 × 10-19 C

1. The ratio of electric force between two electrons to the gravitational force between them is of the order:

(a) 1042

(b) 1039

(c) 1036

(d) 1