21A

YOUR ANSWER:

Both of the above.

(From P1-3B)

Excellent.

You now know what resistance is, the standard symbol for resistance (R), the unit of

measurement for resistance (ohm), the abbreviation for that unit of measurement (), and finally the four factors

that determine resistance.

There is one more item to be discussed while we are on the subject of resistance, and that is specific

resistance. Don't let the big words scare you. It's really very simple. All materials are classified according to the

amount of opposition they offer to current flow. This opposition for any particular material is called its specific

resistance. The standard of measure for all metallic conductors is the resistance in ohms of a conductor that is one

foot long and one mil (.001 inch) in diameter. Since resistance varies with temperature, 20 degrees centigrade has

been set as the temperature at which specific resistance is measured. The standard of measure of nonmetallic

conductors is the centimeter cube. Stated in plainer words, the specific resistance of a nonmetallic conductor is

the amount of resistance, face to face, of a cube of that material, one centimeter long and one centimeter square.

Again, a temperature of 20 degrees centigrade has been set as the standard temperature for measuring specific

resistance. But don't forget that the most important factor in determining the specific resistance of a material is

the atomic structure of that material. Pick the correct statement.

The specific resistance of a material is the

resistance of any amount of that material at

20 degrees centigrade.

Page 1-10A

The specific resistance of a material is the

resistance of a unit volume of that material

at a temperature of 20 degrees centigrade.

Page 1-16A

The specific resistance of a material is the

resistance of that material at 30 degrees

centigrade.

Page 1-18B