Electric Charges and Fields Set-2

Question 1

A cylinder of radius $r$ and length $l$ is placed in a uniform electric field parallel to the axis of the cylinder. The total flux for the surface of the cylinder is given by

Accepted Answer

zero

Answer

$\pi r^2 E$

Answer

$2 \pi r l E$

Answer

$2 \pi r^2 E$

Question 2

Two parallel large thin metal sheets have equal surface charge densities $26.4 	imes 10^{-12} 	ext{ C/m}^2$ of opposite signs. The electric field between these sheets is

Accepted Answer

$3 	ext{ N/C}$

Answer

$3 	imes 10^{-10} 	ext{ N/C}$

Answer

$1.5 	imes 10^{-10} 	ext{ N/C}$

Answer

$1.5 	imes 10^{10} 	ext{ N/C}$

Question 3

A point charge situated at a distance '$r$' from a short electric dipole on its axis, experiences a force $\vec{F}$. If the distance of the charge is '$2r$', the force on the charge will be

Accepted Answer

$\vec{F}/8$

Answer

$\vec{F}/16$

Answer

$\vec{F}/4$

Answer

$\vec{F}/2$

Question 4

The magnitude of the electric field due to a point charge at a distance of $4.0 	ext{ m}$ is $9 	ext{ N/C}$. From the same charged object the electric field of magnitude, $16 	ext{ N/C}$ will be at a distance of

Accepted Answer

$3 	ext{ m}$

Answer

$1 	ext{ m}$

Answer

$2 	ext{ m}$

Answer

$6 	ext{ m}$

Question 5

An electron experiences $\vec{F} = (1.6 	imes 10^{-16} 	ext{ N}) \hat{i}$ in an electric field $\vec{E}$. The electric field is

Accepted Answer

$(-1.0 	imes 10^3 	ext{ N/C}) \hat{i}$

Answer

$(1.0 	imes 10^3 	ext{ N/C}) \hat{i}$

Answer

$(1.0 	imes 10^{-3} 	ext{ N/C}) \hat{i}$

Answer

$(-1.0 	imes 10^{-3} 	ext{ N/C}) \hat{i}$

Question 6

Two charges $q_1$ and $q_2$ are placed at the centres of two spherical conducting shells of radii $r_1$ and $r_2$ respectively. The shells are arranged such that their centres are $d$ $[d > (r_1 + r_2)]$ apart. The force on $q_2$ due to $q_1$ is:

Accepted Answer

$\frac{1}{4\pi\epsilon_0} \frac{q_1 q_2}{d^2}$

Answer

$\frac{1}{4\pi\epsilon_0} \frac{q_1 q_2}{(d-r_1-r_2)^2}$

Answer

zero

Answer

$\frac{1}{4\pi\epsilon_0} \frac{q_1 q_2}{(r_1+r_2)^2}$

Question 7

An electric dipole of length $2 	ext{ cm}$ is placed at an angle of $30^\circ$ with an electric field of $2 	imes 10^5 	ext{ N/C}$. If the dipole experiences a torque of $8 	imes 10^{-3} 	ext{ Nm}$, the magnitude of either charge of the dipole is,

Accepted Answer

$8 \mu 	ext{C}$

Answer

$4 \mu 	ext{C}$

Answer

$7 \mu 	ext{C}$

Answer

$2 \mu 	ext{C}$

Question 8

Assertion (A): A negative charge in an electric field moves along the direction of the electric field. 
Reason (R): On a negative charge a force acts in the direction of the electric field.

Accepted Answer

A is false and R is also false.

Answer

Both A and R are true and R is the correct explanation of A.

Answer

Both A and R are true but R is NOT the correct explanation of A.

Answer

A is true but R is false.

Question 9

Assertion (A): Charge is quantized only integral number of electrons can be transferred. 
Reason (R): There is no possibility of transfer of some fraction of electron.

Accepted Answer

Both A and R are true and R is the correct explanation of A.

Answer

Both A and R are true but R is NOT the correct explanation of A.

Answer

A is true but R is false.

Answer

A is false and R is also false.

Question 10

Assertion (A): In a non-uniform electric field, a dipole will have translatory as well as rotatory motion. 
Reason (R): In a non-uniform electric field, a dipole experiences a force as well as torque.

Accepted Answer

Both A and R are true and R is the correct explanation of A.

Answer

Both A and R are true but R is NOT the correct explanation of A.

Answer

A is true but R is false.

Answer

A is false and R is also false.

Question 11

Assertion (A): Electrostatic field lines start at positive charges and end at negative charges. Reason (R): Field lines are continuous curves without any breaks and they form closed loop.

Accepted Answer

A is true but R is false.

Answer

Both A and R are true and R is the correct explanation of A.

Answer

Both A and R are true but R is NOT the correct explanation of A.

Answer

A is false and R is also false.

Question 12

Assertion (A): Electrons moves away from a region of lower potential to a region of higher potential. Reason (R): An electron has a negative charge.

Accepted Answer

Both A and R are true and R is the correct explanation of A.

Answer

Both A and R are true but R is NOT the correct explanation of A.

Answer

A is true but R is false.

Answer

A is false and R is also false.

Question 13

Assertion (A): All the charge in a conductor gets distributed on whole of its outer surface. Reason (R): In a dynamic system, charges try to keep their potential energy minimum.

Accepted Answer

A is true but R is false.

Answer

Both A and R are true and R is the correct explanation of A.

Answer

Both A and R are true but R is NOT the correct explanation of A.

Answer

A is false and R is also false.

Question 14

Assertion (A): When a body acquires negative charge, its mass decreases. Reason (R): A body acquires positive charge when it gains electrons.

Accepted Answer

A is false and R is also false.

Answer

Both A and R are true and R is the correct explanation of A.

Answer

Both A and R are true but R is NOT the correct explanation of A.

Answer

A is true but R is false.

Question 15

Assertion (A): Surface charge density of an irregularly shaped conductor is non-uniform. Reason (R): Surface density is defined as charge per unit area.

Accepted Answer

Both A and R are true but R is NOT the correct explanation of A.

Answer

Both A and R are true and R is the correct explanation of A.

Answer

A is true but R is false.

Answer

A is false and R is also false.

Question 16

Assertion (A): Total flux through a closed surface is zero if no charge is enclosed by the surface. Reason (R): Gauss law is true for any closed surface, no matter what its shape or size is.

Accepted Answer

Both A and R are true but R is NOT the correct explanation of A.

Answer

Both A and R are true and R is the correct explanation of A.

Answer

A is true but R is false.

Answer

A is false and R is also false.

Question 17

Assertion (A): If a proton and an electron are placed in the same uniform electric field, they experience different acceleration. 
Reason (R): Electric force on a test charge is independent of its mass.

Accepted Answer

Both A and R are true but R is NOT the correct explanation of A.

Answer

Both A and R are true and R is the correct explanation of A.

Answer

A is true but R is false.

Answer

A is false and R is also false.

Question 18

The Electric flux through the surface (enclosing the same point charge $q$)

Accepted Answer

is the same for all the figures.

Answer

in Fig. (iv) is the largest.

Answer

in Fig. (ii) is the least.

Answer

in Fig. (ii) is same as Fig. (iii) but is smaller than Fig. (iv)

Question 19

A hemisphere is uniformly charged positively. The electric field at a point on a diameter away from the centre is directed

Accepted Answer

perpendicular to the diameter

Answer

parallel to the diameter

Answer

at an angle tilted towards the diameter

Answer

at an angle tilted away from the diameter

Question 20

An electric dipole placed in a non-uniform electric field can experience

Accepted Answer

always a force and a torque.

Answer

a force but not a torque.

Answer

a torque but not a force.

Answer

neither a force nor a torque.

Question 21

Figure shows electric field lines in which an electric dipole $\vec{p}$ is placed as shown. Which of the following statements is correct?

Accepted Answer

the dipole will experience a force towards left.

Answer

the dipole will not experience any force.

Answer

the dipole will experience a force towards right.

Answer

the dipole will experience a force upwards.

Question 22

A point charge $+q$, is placed at a distance $d$ from an isolated conducting plane. The field at a point $P$ on the other side of the plane is

Accepted Answer

directed perpendicular to the plane and away from the plane.

Answer

directed perpendicular to the plane but towards the plane.

Answer

directed radially away from the point charge.

Answer

directed radially towards the point charge.

Question 23

If $\oint \vec{E} \cdot d\vec{S} = 0$ over a surface, then

Accepted Answer

the number of flux lines entering the surface must be equal to the number of flux lines leaving it.

Answer

the electric field inside the surface and on it is zero.

Answer

the electric field inside the surface is necessarily uniform.

Answer

all charges must necessarily be outside the surface.

Question 24

The electric field inside a charged conductor is zero because:

Accepted Answer

Charges reside on the surface of a conductor.

Answer

Charges are tightly bound to the nuclei.

Answer

The electric field acts normally to the surface.

Answer

Electric field lines form closed loops.

Question 25

When two different bodies are rubbed against each other, electrons are transferred from the material with:

Accepted Answer

lower work function to the material with higher work function.

Answer

higher work function to the material with lower work function.

Answer

higher mass to the material with lower mass.

Answer

higher permittivity to the material with lower permittivity.

Question 26

In the process of charging by friction, if a glass rod is rubbed with silk cloth, the glass rod becomes positively charged because:

Accepted Answer

It transfers electrons to the silk cloth.

Answer

It gains protons from the silk cloth.

Answer

It gains electrons from the silk cloth.

Answer

It transfers protons to the silk cloth.

Question 27

An electric dipole, when held at $30^\circ$ with respect to a uniform electric field of $10^4 	ext{ N/C}$, experiences a torque of $9 	imes 10^{-26} 	ext{ Nm}$. The magnitude of the dipole moment is:

Accepted Answer

$1.8 	imes 10^{-29} 	ext{ C m}$

Answer

$9 	imes 10^{-30} 	ext{ C m}$

Answer

$4.5 	imes 10^{-30} 	ext{ C m}$

Answer

$1.8 	imes 10^{-26} 	ext{ C m}$

Question 28

What is the value of the proportionality constant $k$ in Coulomb's law $\left(F = k \frac{q_1 q_2}{r^2}\right)$ in free space?

Accepted Answer

$9 	imes 10^9 	ext{ Nm}^2	ext{C}^{-2}$

Answer

$8.85 	imes 10^{-12} 	ext{ C}^2	ext{N}^{-1}	ext{m}^{-2}$

Answer

$1.6 	imes 10^{-19} 	ext{ C}$

Answer

$6.67 	imes 10^{-11} 	ext{ Nm}^2	ext{kg}^{-2}$

Question 29

When an electric dipole is placed in a uniform electric field, the net force acting on it is:

Accepted Answer

Zero

Answer

$qE$

Answer

$2qE$

Answer

Dependent on angle $	heta$

Question 30

The ratio of the magnitude of the electrostatic force to the gravitational force between an electron and a proton is approximately:

Accepted Answer

$10^{39}$

Answer

$10^{19}$

Answer

$10^{-39}$

Answer

$10^{42}$

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Electric Charges and Fields Set-2

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