Here are some things to do to finish this section.

• What question did you think of that could be studied, or observation could you make that is interesting or unexpected? Send it to the Question board!

1. We have many motors around the house that are plugged into the wall socket which provides alternating current.
   • Explain why the kind of motor you made (that runs on a battery) will not work with alternating current. (Do not try to use 110V AC from the wall socket with your motor!! The voltage is too high, and your motor will turn red hot and melt! The question assumes we have used a transformer to produce 3V AC).
   There are three ways to use alternating current to run a motor:
   1. You can convert the AC into DC, using a circuit element that will only allow current to flow one way. Then you can use a motor like the one you built. This is what is done in low-power devices such as electric toothbrushes.
   2. You can have a permanent magnet rotating in the field of an electromagnet driving by AC. Since the field keeps on changing direction, the permanent magnet has to keep on rotating. This is the kind of motor in clocks.
   3. You can have an electromagnet that rotates in the field of a stationary electromagnet. The design would be just like the motor you made, except that the permanent magnet would be replaced by an electromagnet. This is the kind of motor that is used in larger appliances.
   Discuss the advantages and disadvantages of these different designs. Why can't we use the second kind of motor for everything? How does the third kind of motor avoid the problems caused by having alternating current?
2. There are several ways to turn electrical energy into mechanical energy, and thereby turn an electrical signal into an action. The most common is to make use of an electromagnet -- though it may be called a "solenoid" or "actuator." Give some practical examples of how electromagnets are used (or places where you suspect they are being used).
3. You don't usually observe sparks or get a shock from a flashlight battery. But you will see little blue sparks if you look carefully at certain kinds of electrical equipment -- doorbells and motors, for example -- and you can give yourself a small shock (just a tingle, really) while playing with an electromagnet. Explain how to make this happen (or how to avoid it!).

This is the end of this section. (Check this box )   The next section is a summary of the course on Electricity and Magnetism.