22A
YOUR ANSWER:
Resistance is a measure of the opposition of a particular volume of
material at a temperature of 20 degrees centigrade.
NO! NO! NO! That is part of the definition of specific resistance. The full definition goes like this: The specific
resistance of a material is the resistance of a unit volume of that material at a temperature of 20 degrees
centigrade. Now go back and read the statements on Page 1-5A again.
22B
YOUR ANSWER:
Fixed, tapped, and variable is exactly right. DON'T FORGET THE
(From P1-24A)
SCHEMATIC SYMBOLS!
Variable resistors are of two kinds, RHEOSTATS or POTENTIOMETERS. Some variable resistors have
only two terminals and these can only be used as rheostats. A three-terminal variable resistor connected as a
rheostat has only two leads connected to the electrical circuit to adjust the current flow in a circuit or a portion of
a circuit.
If the three terminals of a variable resistor each connect to different parts of a circuit, it is connected as a
potentiometer. A potentiometer does not vary the total resistance between the terminal ends; instead, it varies the
amount of resistance between each end and the center contact. The potentiometer is usually smaller in physical
size than a rheostat and its purpose is to vary the amount of voltage applied to an electrical device. Essentially, it
is a voltage divider.
Complete the statements below by filling in the blanks.
a. The two kinds of variable resistors are the
and
.
b. The purpose of a rheostat is to adjust the
.
c. The purpose of a potentiometer is to vary the
.
(Continued on Page 1-25)
IT0340
1-22
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