1. Three bar magnets are placed near each other along a line, end to end, on a table. The net magnetic force on the middle one is zero, and its north pole is to the left. Make two sketches showing the possible arrangements of the poles of the other magnets.

3. What happens to a ferromagnetic material when it is placed in a magnetic field?

5. Describe the three basic interactions between electricity and magnetism.

7. Name five different basic devices that use at least one of the electromagnetic interactions.

9. To test whether a material is a superconductor, a scientist decides to make a ring out of the material and then to see whether a current will flow around in the ring with no steady energy input.

(a) Explain how a magnet could be used to initiate the current.

(b) At some later time, how could the scientist check to see whether the current is still flowing in the ring without touching the ring?

13. Explain why a transformer doesn't work with DC.

17. Explain how electromagnetic waves are a natural outcome of the principles of electromagnetism.

19. List the main types of electromagnetic waves in order of increasing frequency. Give at least one useful application for each type of wave.

21. What are the main uses of microwaves? Explain how each process works.