Question 1

Which of the following statements best explains why the aurora (as seen in the first image) occurs near the Earth's poles?

Accepted Answer

Charged particles from the sun are trapped by Earth's magnetic field, spiraling along field lines and colliding with atmospheric gases near the poles.

Question 2

What happens when a bar magnet is cut in half, as shown in the second image?

Accepted Answer

Each half becomes a weaker but complete magnet, each with a north and a south pole.

Question 3

Which of the following best describes the interaction between two bar magnets with like poles facing each other, as shown in the third image?

Accepted Answer

They repel each other.

Question 4

A bar magnet is used to pick up paper clips, as shown in the fourth image. What property of the paper clips allows this to happen?

Accepted Answer

Paper clips are made of a ferromagnetic material, allowing their domains to align with the magnet.

Question 5

When a bar magnet is brought near an electroscope, as shown in the fifth image, there is no effect. What does this demonstrate?

Accepted Answer

Magnetic fields do not exert forces on stationary electric charges.

Question 6

A compass needle aligns itself with the Earth's magnetic field, as shown in the sixth image. What does this indicate about the Earth's geographic and magnetic poles?

Accepted Answer

The Earth's geographic north pole is actually a magnetic south pole.

Question 7

Which of the following is true about magnetic field lines around a bar magnet?

Accepted Answer

They form closed loops, exiting the north pole and entering the south pole outside the magnet, and continuing through the magnet.

Question 8

A long, straight wire carries a current $$I. $$What is the expression for the magnetic field strength $$B at a $$distance $$r$$ from the wire?

Accepted Answer

$$B = \frac{\mu_0$ I}{2\pi r}$$

Question 9

A solenoid is constructed with $$N$$ turns, length $$L$$, and carries current $$I. $$What is the formula for the magnetic field inside the solenoid?

Accepted Answer

$$B = \frac{\mu_0$ N I}{L}$$

Question 10

A proton moves with velocity $$\vec{v}$$ perpendicular to a uniform magnetic field $$\vec{B}. $$What is the magnitude of the magnetic force on the proton?

Accepted Answer

$$F = qvB$$

Question 11

A wire of length $$L$$ carries a current $$I$$ perpendicular to a magnetic field $$B. $$What is the magnitude of the force on the wire?

Accepted Answer

$$F = ILB \sin 	heta$$

Question 12

A current loop of area $$A$$ and current $$I is $$placed in a uniform magnetic field $$B at an $$angle $$	heta. $$What is the expression for the torque on the loop?

Accepted Answer

$$	au = IAB \sin 	heta$$

Question 13

A charged particle moves in a circle of radius $$r in a $$uniform magnetic field $$B. $$What is the relationship between the radius, the particle's mass $$m$$, charge $$q$$, and speed $$v$$?

Accepted Answer

$$r = \frac{mv}{qB}$$

Question 14

Which of the following materials is most likely to be strongly attracted to a magnet and can be magnetized?

Accepted Answer

Iron

Question 15

A DC power line runs east-west near the equator, where the Earth's magnetic field points north. What direction must the current flow to produce an upward magnetic force on the wire?

Accepted Answer

East

Question 16

If a current-carrying wire is placed parallel to a uniform magnetic field, what is the magnitude of the magnetic force on the wire?

Accepted Answer

$$F = 0$$

Question 17

Which of the following best describes why permanent magnets cannot have only a north or only a south pole?

Accepted Answer

Cutting a magnet always results in two smaller dipoles, each with a north and south pole.

Question 18

Which of the following is a correct statement about the torque on a magnetic dipole in a uniform magnetic field?

Accepted Answer

The torque is zero when the dipole moment is parallel or antiparallel to the field.

Magnetic Fields and Forces: A Comprehensive Study Guide

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