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!

Part of the sign on the back of a computer monitor. It says it can be used in a 100-to-120 V system, and will draw 1.8A, or in a 220-to-240 V system, and then it will draw 1.0 A.

1. Electrical appliances usually have a little placard on the back or bottom giving their electrical ratings, specifying voltage (V) and either current (A) or wattage (W) (or possibly both). (It also tells the frequency (Hz or cycles); this is of less interest to us at the moment). Please make a table of the information for various devices. (Here is a blank table that you can print out)
   Judging from your table, what are the implications of a device with a very large current rating?
   Houses have fuses or circuit breakers that act like switches to disconnect any device that is drawing a current that is too large -- for example, more than 15 Amperes. You probably did not find any device with a current rating that is this high -- so why do we need the circuit breaker?
   

   This label on a heater gives both current and wattage information.	The label on the bottom of a toaster

   
   
2. In your kit you will find a small piece of thermal sensing sheet. It is a kind of thermometer, that is probably black at room temperature but will turn green or blue when you touch it (or if it is rather warm in the room). When you are through playing with it, let it cool back to a uniform color. Meanwhile, cut a piece of aluminum foil that is 1/2 cm wide and 10 cm long. Straight is OK, but it is more fun if it is somewhat curvey. We are going to use this as a wire. Place the thermal sensing sheet on top of the aluminum foil wire, so that the two ends of the wire stick out. Attach wires with clip ends to the battery, and then to the ends of the aluminum foil, to make the circuit diagrammed at left. Explain what happens.
   
   Notice that what we have made here is an example of the circuit (sometimes called "a short circuit"), which you were warned not to make. What's wrong with a short circuit?

This is the end of this unit. (Check this box )   The next section is about current direction