140. The Effects of Heat.—There are five important changes produced by heat: (a) change of size, (b) change of temperature, (c) change of state, as the melting of ice or evaporating of water, (d) chemical change, as the charring of sugar when it is overheated, and (e) electrical change. This is illustrated by the production of an electric current, by the heating of the junction of two different metals. A thermo-electric generator (see Fig. 122) has been constructed upon this principle and works successfully.
Fig. 122.—A thermo-electric generator.
Important Topics
1. Importance of a study of heat.
2. Four sources of heat.
3. Five effects of heat.
4. Examples of each.
5. Illustrations of transformation of energy which involve heat.