Grade 12 : Physics - Electric Charges and Field (Set 3)

Question 1

Two point charges $q_1 = 2\mu C$and$q_2 = -4\mu C$are separated by10 cm. What is the magnitude of the electrostatic force between them?

Accepted Answer

A) 7.2 N

Answer

B) 3.6 N

Answer

C) 1.8 N

Answer

D) 0.72 N

Question 2

Assertion (A): The electric flux through a closed surface depends on the shape of the surface. Reason (R): Gauss's law states that total flux is $\frac{q_{enclosed}}{\epsilon_0}$.

Accepted Answer

B) Both A and R are true but R is not the correct explanation.

Answer

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

Answer

C) A is true, R is false.

Answer

D) A is false, R is true.

Question 3

An electric dipole is placed in a uniform electric field of $10^5 ext{ N/C}$at an angle of$30^\circ$. If the dipole moment is $2 imes 10^{-6}cm$, calculate the torque.

Accepted Answer

C) 0.1 Nm

Answer

A) 0.2 Nm

Answer

B) 0.05 Nm

Answer

D) 0.4 Nm

Question 4

The electric field at a distance $r$from an infinite line charge of linear charge density$\lambda$is given by?

Accepted Answer

A) $\frac{\lambda}{2\pi \epsilon_0 r}$

Answer

B) $\frac{\lambda}{4\pi \epsilon_0 r}$

Answer

C) $\frac{\lambda}{\epsilon_0 r}$

Answer

D) $\frac{\lambda}{2\pi \epsilon_0 r^2}$

Question 5

What is the electric flux through a sphere of radius $R$enclosing a charge$q$ at its center?

Accepted Answer

B) $\frac{q}{\epsilon_0}$

Answer

A) $\frac{q}{\epsilon_0} 	imes 4\pi R^2$

Answer

C) $\frac{q}{4\pi \epsilon_0 R^2}$

Answer

D) Zero

Question 6

If a charge is moved within an equipotential surface, the work done is?

Accepted Answer

D) Zero

Answer

A) Maximum

Answer

B) Minimum

Answer

C) Positive

Question 7

The unit of surface charge density is?

Accepted Answer

A) $C/m^2$

Answer

B) $C/m$

Answer

C) $C/m^3$

Answer

D) $Nm^2/C$

Question 8

How does the electrostatic force between two charges change if the medium between them has a dielectric constant $K$?

Accepted Answer

B) Decreases by factor $K$

Answer

A) Increases by factor $K$

Answer

C) Remains same

Answer

D) Becomes zero

Question 9

An electric dipole is held in a uniform electric field. The net force on the dipole is?

Accepted Answer

C) Zero

Answer

A) qE

Answer

B) $2qE$

Answer

D) $	au E$

Question 10

The direction of electric field lines is?

Accepted Answer

A) Positive to negative

Answer

B) Negative to positive

Answer

C) Always circular

Answer

D) Towards infinity

Question 11

If the charge on a conductor is doubled, what happens to the intensity of the electric field at a point near it?

Accepted Answer

B) Doubled

Answer

A) Halved

Answer

C) Quadrupled

Answer

D) Unchanged

Question 12

The electrostatic potential at a distance $r$from a point charge$q$ is?

Accepted Answer

C) $\frac{kq}{r}$

Answer

A) $\frac{kq}{r^2}$

Answer

B) $\frac{kq^2}{r}$

Answer

D) kqr

Question 13

Which of the following is not a property of electric field lines?

Accepted Answer

A) They intersect each other

Answer

B) They are continuous curves

Answer

C) They do not form closed loops

Answer

D) The field is stronger where lines are dense

Question 14

Two charges $10\mu C$and$-10\mu C$are at a distance2 cm. Find the dipole moment.

Accepted Answer

B) $2 	imes 10^{-7}cm$

Answer

A) $10^{-7}cm$

Answer

C) $20 	imes 10^{-7}cm$

Answer

D) $5 	imes 10^{-7}cm$

Question 15

The value of permittivity of free space $\epsilon_0$is approximately?

Accepted Answer

D) $8.85 	imes 10^{-12}	ext{ Fm}^{-1}$

Answer

A) $9 	imes 10^9	ext{ Fm}^{-1}$

Answer

B) $8.85 	imes 10^{-11}	ext{ Fm}^{-1}$

Answer

C) $9 	imes 10^{-9}	ext{ Fm}^{-1}$

Question 16

Coulomb's law is valid for which type of charges?

Accepted Answer

A) Point charges

Answer

B) Distributed charges

Answer

C) Moving charges

Answer

D) All of the above

Question 17

The electric field inside a charged spherical conductor is?

Accepted Answer

B) Zero

Answer

A) Maximum

Answer

C) Same as surface

Answer

D) Infinite

Question 18

What is the SI unit of electric flux?

Accepted Answer

C) $Nm^2/C$

Answer

A) Vm

Answer

B) $N/C$

Answer

D) $C^2/Nm^2$

Question 19

If a dipole is placed in a non-uniform electric field, it experiences?

Accepted Answer

A) Both force and torque

Answer

B) Only torque

Answer

C) Only force

Answer

D) Neither

Question 20

Quantization of charge implies that charge on an object can only be?

Accepted Answer

D) An integral multiple of $e$

Answer

A) Any real value

Answer

B) A fraction of $e$

Answer

C) Always positive

Set 3Grade 12 : Physics - Electric Charges and Field