Heat, current flow and resistance

Friday, December 20, 2013

Q. In my course, I have learned that when current flows through a resistance, it produces heat. How does this happen?

A. The kinetic theory of matter says that the atoms in any material at a temperature above absolute zero (-273° C.) move. The greater the temperature, teh greater teh energyh with which the atoms move. In a gas, the atoms are not bound to each other, but bounce of one another and the walls of the container.

In a solid, th eatoms are bound together by shared electrons in their outer orbits. But these bonds are not perfectly rigid. Instead, they have some spring-like "give" to them. This allows each atom to vibrate around a central position in the structure. The greater the temperature, the harder the atoms vibrate. If the temperature is high enough, the atoms vibrate with enough force to break the bonds between them. Then the material melts and becomes a liquid.

When current passes through a material, teh electrons jump from atom to atom. This jostles the atoms, making them vibrate harder. This is another way of saying that the temperature of the material increases. The conversion from electrical energy to thermal energy is very efficient. Practically al the electrical energy delivered to a resistor is converted into heat energy.

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