Q: A rectangular current loop with area $A$ and current $I$ is placed in a uniform magnetic field $\vec{B}$. What is the expression for the torque on the loop?

$\tau = \vec{\mu} \times \vec{B}$, where $\vec{\mu} = IA\hat{n}$

Q: A mass spectrometer uses electric and magnetic fields to separate ions by their mass. Which principle allows it to select ions of a specific velocity?

The Lorentz force law $F = q(E + v \times B)$

Q: A current-carrying wire is placed in a uniform magnetic field. Which equation gives the infinitesimal force on a segment $d\vec{l}$ of the wire?

$d\vec{F} = I d\vec{l} \times \vec{B}$

Question 1

Which of the following best describes the force experienced by a charged particle moving in a uniform magnetic field?

Accepted Answer

The force is always perpendicular to both the velocity and the magnetic field.

Question 2

A proton with charge $q = 1.6 	imes 10^{-19}\ \mathrm{C}$ moves at $v = 3.0 	imes 10^6\ \mathrm{m/s}$ in a uniform magnetic field $B = 2.0\ \mathrm{T}$ at an angle of $30^\circ$ to the field. What is the magnitude of the magnetic force on the proton?

Accepted Answer

$F = qvB \sin 30^\circ$

Question 3

Which law states that the net magnetic flux through any closed surface is zero?

Accepted Answer

Gauss's Law for magnetism

Question 4

A wire of length $L$ carries a current $I$ in a uniform magnetic field $\vec{B}$. The wire is oriented so that its length vector $\vec{L}$ is perpendicular to $\vec{B}$. What is the magnitude of the force on the wire?

Accepted Answer

$F = ILB$

Question 5

A charged particle moves through a region with both electric field $\vec{E}$ and magnetic field $\vec{B}$. What is the total force acting on the particle?

Accepted Answer

$F = q(E + v 	imes B)$

Question 6

A rectangular current loop with area $A$ and current $I$ is placed in a uniform magnetic field $\vec{B}$. What is the expression for the torque on the loop?

Accepted Answer

$	au = \vec{\mu} 	imes \vec{B}$, where $\vec{\mu} = IA\hat{n}$

Question 7

Which of the following real-world devices relies on the principle of magnetic forces on moving charges?

Accepted Answer

MRI scanner

Question 8

A negative charge $q$ moves in the $+x$ direction in a magnetic field $\vec{B} = (3\hat{i} - 4\hat{j})\ \mathrm{T}$. What is the direction of the magnetic force on the charge?

Accepted Answer

In the $-z$ direction

Question 9

If a current-carrying loop is placed in a uniform magnetic field, what orientation will the torque tend to achieve?

Accepted Answer

The plane of the loop will be perpendicular to the magnetic field.

Question 10

Which of the following statements about magnetic field lines is correct?

Accepted Answer

Magnetic field lines are always closed loops and never start or end.

Question 11

A charged particle moves in a circle in a uniform magnetic field. What is the frequency of its motion?

Accepted Answer

$f = \dfrac{qB}{2\pi m}$

Question 12

Which of the following is NOT a consequence of the Lorentz force law?

Accepted Answer

Magnetic fields can do work on charged particles.

Question 13

A straight wire segment of length $L$ carries a current $I$ in the $+x$ direction. The wire is placed in a uniform magnetic field $\vec{B}$ pointing in the $+z$ direction. What is the direction of the magnetic force on the wire?

Accepted Answer

In the $+y$ direction

Question 14

Which of the following best explains why magnets can attract some uncharged objects?

Accepted Answer

Uncharged objects can be polarized by the magnetic field.

Question 15

A mass spectrometer uses electric and magnetic fields to separate ions by their mass. Which principle allows it to select ions of a specific velocity?

Accepted Answer

The Lorentz force law $F = q(E + v 	imes B)$

Question 16

A circular loop of wire with $N$ turns, area $A$, and current $I$ is placed in a uniform magnetic field $\vec{B}$. What is the magnetic dipole moment of the loop?

Accepted Answer

$\mu = NIA$

Question 17

Which of the following is true about the net magnetic flux through a closed surface?

Accepted Answer

It is always zero, regardless of what the surface encloses.

Question 18

A current-carrying wire is placed in a uniform magnetic field. Which equation gives the infinitesimal force on a segment $d\vec{l}$ of the wire?

Accepted Answer

$d\vec{F} = I d\vec{l} 	imes \vec{B}$

Question 19

Which of the following phenomena is NOT directly explained by the interaction of moving charges and magnetic fields?

Accepted Answer

The heating of a resistor in a circuit

Magnetic Field and Magnetic Forces: Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards