Question 1

Which of the following correctly describes the direction of electric field lines around a positive point charge?

Accepted Answer

Electric field lines point radially outward from the charge.

Question 2

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

Accepted Answer

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

Question 3

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

Accepted Answer

$E = \frac{\lambda}{2\pi\epsilon_0 r}$

Question 4

Which principle allows you to calculate the net electric field at a point due to multiple charges?

Accepted Answer

Principle of superposition

Question 5

A water molecule is a permanent dipole. What is the direction of the electric field at a point on the axis of the dipole, far from the molecule?

Accepted Answer

The field points away from the positive end of the dipole.

Question 6

What is the electric field at a distance $z$ along the axis from the center of a ring of radius $R$ carrying total charge $Q$?

Accepted Answer

$E = \frac{Qz}{4\pi\epsilon_0 (z^2 + R^2)^{3/2}}$

Question 7

A parallel plate capacitor has plates with charge $+Q$ and $-Q$. What is the electric field between the plates (ignoring edge effects)?

Accepted Answer

$E = \frac{Q}{\epsilon_0 A}$

Question 8

Which of the following statements about electric field lines is FALSE?

Accepted Answer

Electric field lines can cross each other.

Question 9

A flat circular ring of radius $R$ carries a total charge $Q$ uniformly distributed. What is the surface charge density $\sigma$?

Accepted Answer

$\sigma = \frac{Q}{2\pi R^2}$

Question 10

Two protons, A and B, are in a uniform electric field. Proton A is twice as massive as proton B. Which proton has the larger acceleration?

Accepted Answer

Proton B

Question 11

What is the SI unit of the electric field?

Accepted Answer

Newton per Coulomb (N/C)

Question 12

A thin rod of length $L$ carries a total charge $Q$ uniformly distributed. What is the linear charge density $\lambda$?

Accepted Answer

$\lambda = \frac{Q}{L}$

Question 13

Which equation gives the electric field at a point on the bisecting plane of a dipole at distance $r$ from the center?

Accepted Answer

$E_{dipole} = -\frac{1}{4\pi\epsilon_0} \frac{p}{r^3}$

Question 14

A sphere of charge $Q$ and radius $R$ produces an electric field outside the sphere that is:

Accepted Answer

Identical to the field of a point charge $Q$ at the center.

Question 15

What is the $y$-component of the electric field at the dot due to the shaded region of charge on a rod of length $L$ and total charge $Q$?

Accepted Answer

$\frac{Q}{L} \frac{y}{4\pi\epsilon_0 (x^2 + y^2)} dx$

Question 16

Which of the following best describes the electric field inside a uniformly charged spherical shell?

Accepted Answer

The field is zero everywhere inside the shell.

Question 17

A dipole is placed in a uniform electric field. What happens to the dipole?

Accepted Answer

It experiences a torque but no net force.

Question 18

Which of the following is the correct expression for the electric field at a distance $r$ from an infinite plane of charge with surface charge density $\eta$?

Accepted Answer

$E = \frac{\eta}{2\epsilon_0}$

Question 19

An electron is placed in the plane that bisects a dipole. What is the direction of the electric force on the electron?

Accepted Answer

Away from the dipole along the bisecting plane.

Electric Fields: Point Charges, Dipoles, Continuous Distributions, and Field Lines

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