Q: A dipole is placed in a uniform electric field. What is the torque experienced by the dipole?

$\tau = \mathbf{p} \times \mathbf{E}$

Q: Which equation expresses Gauss’s law for a closed surface $S$?

$\phi = \frac{q}{\varepsilon_0}$

Question 1

Which of the following statements best describes the principle of superposition in electrostatics?

Accepted Answer

The force on a charge due to multiple other charges is the vector sum of the forces due to each charge, unaffected by the presence of other charges.

Question 2

A glass rod is rubbed with silk. Which statement correctly explains the resulting charges?

Accepted Answer

Electrons are transferred from the glass rod to the silk, making the rod positively charged and the silk negatively charged.

Question 3

Which equation represents the quantisation of electric charge?

Accepted Answer

$q = n e$

Question 4

If two point charges $q_1$ and $q_2$ are separated by a distance $r$ in vacuum, what is the magnitude of the force between them according to Coulomb’s law?

Accepted Answer

$F = \frac{1}{4 \pi \varepsilon_0} \frac{q_1 q_2}{r^2}$

Question 5

Which property distinguishes conductors from insulators?

Accepted Answer

Conductors have free electrons that can move throughout the material, while insulators do not.

Question 6

A charged comb attracts small pieces of paper. Which explanation is correct?

Accepted Answer

The comb polarises the paper, inducing a dipole moment, and the non-uniform electric field exerts a net force on the paper.

Question 7

What is the electric field at a distance $r$ from a point charge $Q$ in vacuum?

Accepted Answer

$E = \frac{1}{4 \pi \varepsilon_0} \frac{Q}{r^2}$

Question 8

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

Accepted Answer

Electric field lines can cross each other.

Question 9

A dipole is placed in a uniform electric field. What is the torque experienced by the dipole?

Accepted Answer

$	au = \mathbf{p} 	imes \mathbf{E}$

Question 10

Which equation defines the electric flux $\phi$ through an area element $\Delta S$?

Accepted Answer

$\phi = \mathbf{E} \cdot \Delta \mathbf{S}$

Question 11

A thin spherical shell of radius $R$ carries a uniform surface charge density $\sigma$. What is the electric field at a point inside the shell ($r < R$)?

Accepted Answer

$E = 0$

Question 12

Which equation expresses Gauss’s law for a closed surface $S$?

Accepted Answer

$\phi = \frac{q}{\varepsilon_0}$

Question 13

A long, straight wire has a uniform linear charge density $\lambda$. What is the electric field at a distance $r$ from the wire?

Accepted Answer

$E = \frac{\lambda}{2 \pi \varepsilon_0 r}$

Question 14

Which of the following best describes the electric field due to a dipole at large distances ($r \gg a$)?

Accepted Answer

It falls off as $1/r^3$.

Question 15

A point charge $q$ is placed at the centre of a sphere of radius $r$. What is the total electric flux through the sphere?

Accepted Answer

$\phi = \frac{q}{\varepsilon_0}$

Question 16

Which of the following is a correct statement about the conservation of electric charge?

Accepted Answer

The total charge of an isolated system remains unchanged with time.

Question 17

A molecule of water (H$_2$O) contains 10 protons and 10 electrons. What is the net charge of a water molecule?

Accepted Answer

Zero, because the positive and negative charges cancel each other.

Question 18

Which of the following is the correct unit for electric field in SI units?

Accepted Answer

N/C

Question 19

If a system contains five charges: +1, +2, –3, +4, and –5 (in arbitrary units), what is the total charge?

Accepted Answer

-1

Electric Charges and Fields: Structured Study Notes

Study Guide - Practice Questions

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