# AP Physics 2 : Other Magnetism Concepts

## Example Questions

### Example Question #1 : Other Magnetism Concepts

Which of the following is not likely to cause a magnet to lose strength?

All of these will cause a magnet to lose strength

Heating the magnet

Striking the magnet with a hammer

Cooling the magnet

Dropping the magnet on the floor

Cooling the magnet

Explanation:

Magnetism is caused by electrons in a material aligning and causing an aggregate magnetic field that can exert influence over other things. The magnetic strength is limited by random fluctuations in the electrons, making them no longer aligned. If the magnet were to be cooled, the electrons would have less kinetic energy, and would be less likely to have random fluctuations. This would make the strength increase.

All of the other things would make the strength of a magnet decrease. Striking it would impart kinetic energy, and would momentarily vibrate the electrons. Likewise, heating it would make the electrons vibrate more.

### Example Question #2 : Other Magnetism Concepts

Suppose there is a velocity filter than can detect a particle's speed at the instant where the electric force is equal to the magnetic force. In order to increase the particle's speed, which of the following factors should be changed?

Increased magnetic field

Increased electric field

Increased charge of the particle and magnetic field

Increased magnetic field and electric field

Increased charge of the particle

Increased electric field

Explanation:

In this question, we're told that the velocity filter is able to detect the speed of a particle when the magnetic force and electric force are equal to each other. In order to determine when the particle's velocity will be the greatest, we'll need to keep in mind the equations for both the electric force and magnetic force:

Next, we'll need to set them equal to each other:

Then, we can isolate the velocity term:

Based on this equation, we see that if we want to increase the particle's velocity, we'll need to increase the electric field. Increasing the particle's charge will have no effect on the particle's velocity, and increasing the magnetic field will actually decrease the particle's velocity.

### Example Question #2 : Other Magnetism Concepts

Which of the following scenarios would not result in a lower overall magnetic field?

Dropping a permanent magnet on the floor

Cooling a permanent magnet

Adding an external magnetic field to a diamagnet

All of these scenarios lower the effective magnetic field.

Heating a permanent magnet

Cooling a permanent magnet

Explanation:

The magnetic field around permanent magnets is caused by the alignment of the material's electrons, which no longer average out to a net field of zero and instead combine to form a greater field. If the electrons come out of alignment, then the field wanes or stops altogether. Additionally, the random vibrations of the electrons inhibits the effectiveness of the field. Therefore, if you were to apply energy to a magnet, it would be less effective because the electrons would have greater random motion. Heating the magnet applies thermal energy to it, and dropping it applies kinetic energy to it, which means neither of them would be the right answer. When you cool a magnet, you are removing some of the energy it has, making the electrons have less random motion.

A diamagnet is a material that, when it is exposed to a magnetic field, produces a magnetic field in the opposite direction as the external field, which leaves an overall lesser field.