Elenco Basic Electronic Experiments - Manual (Page 11)

The Variable Resistor: We talked about how a switch is used to turn the electricity on and off just like a valve is used to
turn the water on and off. But there are many times when you want some water but don’t need all that the pipe can deliver,
so you control the water by adjusting an opening in the pipe with a faucet. Unfortunately, you can’t adjust the thickness of
an already thin wire. But you could also control the water flow by forcing the water through an adjustable length of rocks,
as in the rock arm shown below.
In electronics we use a variable resistor. This is a normal resistor (50k
Ω in your PK-101) with an additional arm contact
that can move along the resistive material and tap off the desired resistance.
The dial on the variable resistor moves the arm contact and sets the resistance between the left and center pins. The
remaining resistance of the part is between the center and right pins. For example, when the dial is turned fully to the left,
there is minimal resistance between the left and center pins (usually 0
Ω) and maximum resistance between the center and
right pins. The resistance between the left and right pins will always be the total resistance, (50k
Ω for your part).
Now let’s demonstrate how this works.
11
ROCK
ARM
VARIABLE RESISTOR
Symbol for VARIABLE RESISTOR
CENTER PIN
RIGHT PIN LEFT PIN
WIPER CONTACT
INSULATING BASE MATERIAL
LEADS
MOVABLE
ARM
THIN LAYER OF
RESISTIVE MATERIAL
STATIONARY CONTACT
VARIABLE RESISTOR