Question 1

Which of the following statements best explains why breaking a bar magnet in half does NOT produce isolated magnetic poles?

Accepted Answer

Each half becomes a new magnet with both a north and a south pole.

Question 2

A nail is attracted to either end of a bar magnet, as shown in the images. What does this demonstrate about the nature of magnetic poles?

Accepted Answer

Both the north and south poles of a magnet attract unmagnetized iron objects.

Question 3

Which of the following best describes the force between two bar magnets placed with their north poles facing each other?

Accepted Answer

The magnets will repel each other.

Question 4

Which of the following equations correctly gives the magnitude of the magnetic force on a charge $$q$$ moving with velocity $$\vec{v} in a $$magnetic field $$\vec{B}$$?

Accepted Answer

$$F = |q| v B \sin 	heta$$

Question 5

A proton moves at $$3.0 	imes 10^5$ m/s in a uniform 2.0$ T magnetic field directed along the positive z$-axis. The velocity of the proton makes a 30$$^\circ$$ angle with the +z$-axis. What is the magnitude of the force on the proton?

Accepted Answer

$$4.8 	imes 10$$^{-14}$$ N

Question 6

A charge $$q$$ moves parallel to a uniform magnetic field $$\vec{B}. $$What is the magnetic force acting on the charge?

Accepted Answer

$$0$$

Question 7

Which rule is used to determine the direction of the magnetic force on a positive moving charge in a magnetic field?

Accepted Answer

Right-hand rule

Question 8

A negatively charged particle moves in a magnetic field. How does the direction of the magnetic force compare to that for a positive charge moving in the same direction?

Accepted Answer

The force is in the opposite direction.

Question 9

A compass needle points north when placed near a wire with no current. What happens when a current flows through the wire?

Accepted Answer

The compass needle deflects, and the direction depends on the current's direction.

Question 10

Which of the following best describes the Earth's magnetic field?

Accepted Answer

It resembles the field of a bar magnet tilted with respect to the geographic axis.

Question 11

What is the SI unit of the magnetic field, and how is it defined in terms of other units?

Accepted Answer

Tesla (T), where $$1\ \mathrm{T} = 1\ \mathrm{N}/(\mathrm{A}\cdot\mathrm{m})$$

Question 12

A particle with charge $$-1.24 	imes 10$$^{-8}$$ C moves with velocity $$\vec{v} = (4.0 	imes $$10^4$$\ \mathrm{m/s})\hat{i} + (-3.8 	imes $$10^4$$\ \mathrm{m/s})\hat{j}$$ in a magnetic field $$\vec{B} = (1.5\ \mathrm{T})\hat{i}$$. What is the direction of the magnetic force on the particle?

Accepted Answer

In the $$-\hat{k}$$ direction

Question 13

Which of the following is true about the cross product $$\vec{A} 	imes \vec{B}$$?

Accepted Answer

It is zero if $$\vec{A}$$ and $$\vec{B}$$ are parallel.

Question 14

A student uses the right-hand rule to determine the direction of the force on a positive charge moving in a magnetic field. Which step is INCORRECT?

Accepted Answer

Using the left hand instead of the right hand.

Question 15

A charged particle moves at an angle $$\phi to a $$magnetic field $$\vec{B}. $$Which formula gives the magnitude of the force?

Accepted Answer

$$F = |q| v B \sin \phi$$

Question 16

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

Accepted Answer

They begin and end on electric charges.

Question 17

If a positive charge moves perpendicular to a uniform magnetic field, what is the direction of the magnetic force relative to the velocity and the field?

Accepted Answer

Perpendicular to both the velocity and the magnetic field.

Question 18

Which of the following best describes the effect of the Earth's magnetic field on a compass?

Accepted Answer

The compass needle aligns with the Earth's magnetic field lines.

Magnetic Fields and Magnetic Forces

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