Electric Charges and Fields Set-1

Practice Important MCQs for Electric Charges and Fields — Physics, Class 12.

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Q1. . Two point charges placed in a medium of dielectric constant 5 are at a distance $r$ between them, experience an electrostatic force 'F'. The electrostatic force between them in vacuum at the same distance $r$ will be:

(A)

$5F$

(B)

$F$

(C)

$F/2$

(D)

$F/5$

Q2. In an experiment three microscopic latex spheres are sprayed into a chamber and became charged with charges $+3e$ , $+5e$ and $-3e$ respectively. All the three spheres came in contact simultaneously for a moment and got separated. Which one of the following are possible values for the final charge on the spheres?

(A)

$+5e$ , $-1e$ , $+5e$

(B)

$+6e$ , $+6e$ , $-7e$

(C)

$-4e$ , $+3.5e$ , $+5.5e$

(D)

$+5e$ , $-8e$ , $+7e$

Q3. Two point charges $+8q$ and $-2q$ are located at $x=0$ and $x=L$ respectively. The point on $x$ -axis at which net electric field is zero due to these charges is:

(A)

$8L$

(B)

$4L$

(C)

$2L$

(D)

$L$

Q4. The electric potential $V$ at any point $(x, y, z)$ is given by $V = 3x^2$ where $x$ is in metres and $V$ in volts. The electric field at the point $(1\text{m}, 0.2\text{m})$ is:

(A)

$6 \text{ V/m}$ along $(-\text{x})$ -axis

(B)

$6 \text{ V/m}$ along $(+\text{x})$ -axis

(C)

$1.5 \text{ V/m}$ along $(-\text{x})$ -axis

(D)

$1.5 \text{ V/m}$ along $(+\text{x})$ -axis

Q5. Assertion (A): On going away from a point charge or a small electric dipole, electric field decreases at the same rate in both the cases.
Reason (R): Electric field is inversely proportional to square of distance from the charge or an electric dipole.

(A)

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

(B)

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

(C)

A is true but R is false.

(D)

A is false and R is also false.

Q6. The electric field at $r = R$ (for a non-uniformly distributed nuclear charge $Z e$ within nucleus radius $R$ ) is:

(A)

directly proportional to $a$

(B)

directly proportional to $a^2$

(C)

inversely proportional to $a$

(D)

independent of $a$

Q7. The electric field within the nucleus is generally observed to be linearly dependent on $r$ . This implies:

(A)

$a = 0$

(B)

$a = R/2$

(C)

$a = R$

(D)

$a = 2R/3$

Q8. Electric field intensity at point $P$ due to charge distributed over a sphere is:

(A)

$E = \frac{1}{4\pi \epsilon_0} \frac{q}{r^2}$

(B)

$E = \frac{\sigma R^2}{\epsilon_0 2r^2}$

(C)

$E = \frac{1}{4\pi \epsilon_0} \frac{2q}{r^2}$

(D)

$E = 0$

Q9. When point $P$ is inside a conducting spherical shell:

(A)

$E = 0$

(B)

$E = \frac{1}{4\pi \epsilon_0} \frac{q}{r^2}$

(C)

cannot be calculated

(D)

remains constant everywhere inside the sphere (always non-zero)

Q10. Which statement is true for Gauss's law:

(A)

All the charges whether inside or outside the gaussian surface contribute to the electric flux.

(B)

Electric flux depends upon the geometry of the gaussian surface.

(C)

Gauss's theorem can be applied to non-uniform electric field.

(D)

The electric field over the Gaussian surface remains continuous and uniform at every point.

Q11. Assertion (A): A metallic shield in form of a hollow shell may be built to block an electric field.
Reason (R): In a hollow spherical shield, the electric field inside it is zero at every point.

(A)

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

(B)

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

(C)

A is true but R is false.

(D)

A is false and R is also false.

Q12. A charge 'q' is placed at the center of a cube of side 'l'. What is the electric flux passing through each face of the cube?

(A)

$q / \epsilon_0$

(B)

$q / (6 \epsilon_0)$

(C)

$q / (4 \epsilon_0)$

(D)

$0$

Q13. A thin metallic spherical shell of radius $R$ carries charge $Q$ . A point charge $Q/2$ is placed at its centre $C$ . What is the magnitude of the force on the charge $Q/2$ at the centre?

(A)

$3Q^2 / (8\pi\epsilon_0 R^2)$

(B)

$Q^2 / (4\pi\epsilon_0 R^2)$

(C)

$Q / (4\pi\epsilon_0 R^2)$

(D)

Zero

Q14. A thin metallic spherical shell of radius $R$ carries charge $Q$ . A point charge $+2Q$ is placed outside the shell at point $A$ at a distance $x$ ( $x > R$ ) from the centre $C$ . Assuming the internal charge is $Q/2$ at $C$ , the force exerted by the shell and internal charge on the charge $+2Q$ at point $A$ is:

(A)

$3Q^2 / (8\pi\epsilon_0 x^2)$

(B)

$Q^2 / (4\pi\epsilon_0 x^2)$

(C)

$3Q^2 / (4\pi\epsilon_0 x^2)$

(D)

Zero

Q15. Figure shows six charged lumps of plastic coin. The cross-section of a Gaussian surface $S$ is indicated. What is the net electric flux through the surface?

(A)

$(q_1 - q_2 - q_3 - q_6) / \epsilon_0$

(B)

$(q_1 - q_2 + q_3) / \epsilon_0$

(C)

$(q_1 - q_2 + q_3 - q_6) / \epsilon_0$

(D)

$(q_1 - q_2 + q_3 - q_6 + q_4 + q_5) / \epsilon_0$

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