Online Test: Electrostatics | Class 12 Physics

Question 1 of 20

The elementary charge $e$ equals:

$1.6\times10^{-19}\ \text{C}$

$9\times10^{9}\ \text{C}$

$6.25\times10^{18}\ \text{C}$

$8.85\times10^{-12}\ \text{C}$

Explanation: The elementary charge is $1.6\times10^{-19}\ \text{C}$.

Question 2 of 20

Coulomb force varies with separation as:

$1/r$

$1/r^2$

$r$

$r^2$

Explanation: $F\propto1/r^2$ in Coulomb\u2019s law.

Question 3 of 20

If both charges are doubled and the distance unchanged, the force becomes:

double

four times

half

unchanged

Explanation: $F\propto q_1q_2$, so doubling both gives a factor 4.

Question 4 of 20

Electric field is defined as:

$qF$

$F/q$

$q/F$

$Fq^2$

Explanation: $\vec{E}=\vec{F}/q$, force per unit positive charge.

Question 5 of 20

Field lines of a positive point charge are directed:

radially inward

radially outward

tangentially

in closed loops

Explanation: Lines emanate radially outward from a positive charge.

Question 6 of 20

The dipole moment of $\pm q$ separated by $2a$ is:

$q/2a$

$q(2a)$

$2a/q$

$q^2 a$

Explanation: $p=q\times(2a)$, directed from $-q$ to $+q$.

Question 7 of 20

Torque on a dipole in a uniform field is:

$pE\cos\theta$

$pE\sin\theta$

$pE$

$p/E$

Explanation: $\tau=pE\sin\theta$, maximum at $90^\circ$.

Question 8 of 20

Electric flux through area $A$ in field $E$ at angle $\theta$ to the normal is:

$EA\sin\theta$

$EA\cos\theta$

$EA$

$E/A$

Explanation: $\phi=\vec{E}\cdot\vec{A}=EA\cos\theta$.

Question 9 of 20

Gauss\u2019s law gives total flux as:

$q\epsilon_0$

$q/\epsilon_0$

$\epsilon_0/q$

$q^2/\epsilon_0$

Explanation: $\oint\vec{E}\cdot d\vec{A}=q_{enc}/\epsilon_0$.

Question 10 of 20

The field of an infinite charged sheet is:

$\sigma/\epsilon_0$

$\sigma/2\epsilon_0$

$2\sigma/\epsilon_0$

$\sigma\epsilon_0$

Explanation: $E=\sigma/2\epsilon_0$, uniform.

Question 11 of 20

Inside a uniformly charged spherical shell the field is:

maximum

zero

constant nonzero

infinite

Explanation: No charge is enclosed, so $E=0$ inside.

Question 12 of 20

Potential due to a point charge varies as:

$1/r^2$

$1/r$

$r$

$r^2$

Explanation: $V=\frac{1}{4\pi\epsilon_0}\frac{q}{r}\propto1/r$.

Question 13 of 20

Electric potential is a:

vector

scalar

tensor

pseudovector

Explanation: Potential is a scalar; contributions add algebraically.

Question 14 of 20

The relation between field and potential is:

$E=Vr$

$E=-\frac{dV}{dr}$

$E=V/r^2$

$E=\frac{dr}{dV}$

Explanation: The field is the negative potential gradient.

Question 15 of 20

Work done in moving a charge on an equipotential surface is:

positive

negative

zero

infinite

Explanation: $V$ is constant, so $W=q\Delta V=0$.

Question 16 of 20

Capacitance is defined as:

$QV$

$Q/V$

$V/Q$

$Q^2V$

Explanation: $C=Q/V$, unit farad.

Question 17 of 20

For a parallel-plate capacitor $C=$

$\epsilon_0 d/A$

$\epsilon_0 A/d$

$Ad/\epsilon_0$

$\epsilon_0 Ad$

Explanation: $C=\frac{\epsilon_0 A}{d}$.

Question 18 of 20

Energy stored in a capacitor is:

$\frac12 CV$

$\frac12 CV^2$

$CV^2$

$C^2V$

Explanation: $U=\frac12 CV^2=\frac{Q^2}{2C}$.

Question 19 of 20

In series the equivalent capacitance is:

the sum

less than the smallest

greater than the largest

the average

Explanation: $\frac{1}{C_s}=\sum\frac{1}{C_i}$.

Question 20 of 20

A dielectric of constant $K$ changes capacitance $C_0$ to:

$C_0/K$

$KC_0$

$C_0$

$K^2 C_0$

Explanation: $C=KC_0$.

Online Test — Electrostatics