Lesson 1/Learning Event 2
The amount of resistance that a resistor or any other conductor offers to current flow is measured
in OHMS. A material has 1 ohm of resistance when 1 volt (pressure) will force 1 ampere of
current to flow through it. Resistance is measured with an OHMMETER, which will be covered
later.
RELATIONSHIP OF QUANTITIES IN AN ELECTRICAL CIRCUIT
There is a definite relationship between voltage, resistance, and amperage that must be considered
when maintaining automotive electrical systems. From the example of the light bulb, you can see
that whether or not the bulb works as it should depends on the amount of current that is flowing
through the circuit. From our study up to now, you can also see that a change in either the
amount of voltage or the amount of resistance will change the amount of current flowing in a
circuit. Here are some facts about changes in voltage, resistance, and amperage that you should
remember.
If the voltage in a circuit is made higher and the resistance remains the same, the amperage
(current) will also get higher. The reverse of this is also true--less voltage will cause less amperage.
If more resistance is put in an electrical circuit, the current is reduced whereas less resistance allows
more current to flow.
Resistance can be changed by changing the length or diameter of a wire, by using a rheostat, or by
using different sizes of fixed resistors.
ALTERNATING CURRENT
The electricity that comes to your home for operating the lights, refrigerators, and so forth, is
ALTERNATING CURRENT (AC). It was given this name because the electrons move through
the wire first in one direction and then in the opposite direction. Since current flows from negative
(surplus of electrons) to positive (shortage of electrons), the generating plant producing an
alternating current must be periodically changing the electrical charge. In this manner, the electrons
are caused to move back and forth in the circuit instead of in a constant stream moving in one
direction only.
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