Now we know that heat is not a material. It does not take up space. It does not weigh anything. Instead, it is a form of energy. And when we say that heat is a form of energy, we mean that it can be used to do work. What to Do 1. Make a simple resistance heater. 2. Make some popcorn by: (a) conduction (b) convection (c) radiation "Resistance" Makes Heat There are at least four ways that electricity can make heat. The one that we'll cover here is _resistance_ heating. (The others are: _dielectric_ heating, where the lines of force of an electrostatic field pass through a non-conductive material and heat it; the _heat pump_, which is a refrigerator in reverse; and _electronic_ heating, which uses high frequency waves similar to radio waves to create high speed movement of the molecules or tiny particles which rub together to make heat.) _Resistance_ heating occurs because every conductor of electricity opposes the flow of current through it. Some conductors resist more than others. When they do, a certain amount of warming takes place. The more resistance that is offered, the more heating there is. Some materials, like silver, copper, and aluminum, offer little resistance. We say they are good conductors. Other materials, like iron, offer more resistance. They are still conductors, but not as good as the others mentioned. The _size_ of the conductor, and its _length_ are the other two things that affect its resistance. The _smaller_ it is, the greater its resistance. Also, the _longer_ it is, the greater its resistance. Therefore, when we only want to _move_ electricity from place to place, we want relatively large, "good" conductors. Here, we do not want to make heat. In fact, we want to avoid it, because too much heat in the wrong place can cause a fire. But when we want heat, we choose relatively small, "poor" conductors, and the more heat we want, the longer they must be. If you will think of the filament inside a lamp bulb; you may recall that it is a very fine wire, coiled so as to get a maximum length, and made of tungsten which has a high resistance. Because of all these factors, this filament glows at a white heat, and is a source of both light and heat. Make a Simple Resistance Heater _Materials you will need_: 1 dry cell battery 1 foot iron picture wire Pliers Use a short strand of iron picture wire and hook the ends to the terminals of a dry cell battery. Use pliers so that you do not burn your fingers. Disconnect the wires as soon as they become hot. Tell why the wires heat. Conduction is "Touching" Heat Conduction occurs when you set a pan containing food right on a heating element. An egg cooking in a hot frying pan is a good example of conduction at work. This method is the most efficient single way of using electric heat for cooking. Convection Depends on Air