Objectives
After studying this chapter, you will be
able to answer these questions:
1. What is the relationship between volt-
age, current, and resistance in a circuit?
2. What is Ohm’s law and how can we use
it to solve electrical circuit problems?
3. What types of switches are used in elec-
trical circuits?
Important
Words and Terms
The following words and terms are key
concepts in this chapter. Look for them as
you read this chapter.
The Simple Circuit
Electrical circuits are complete path-
ways through which electric current flows.
Three elements are basic to all circuits:
1. Voltage source (such as a battery or gen-
erator). A device that supplies the energy.
2. Load (such as a resistor, motor, or
lamp). A device that uses energy from
the voltage source.
3. Conductive pathway (such as an insu-
lated wire or printed circuit board). A
path from voltage source to load and
back, which carries electrical current.
Circuits usually contain a fourth element,
as well. A control device such as a switch,
fuse/circuit breaker, or relay may be used
to stop, start, and/or regulate the flow of
electricity.
Figure 4-1 is a schematic diagram of a
simple circuit. The symbols show that the
circuit has a battery for the voltage source; a
load device (resistor), which uses the energy
from the voltage source; an “on/off” switch;
and connecting wire to conduct the current.
Ohm’s Law
One of the basic laws of electrical cir-
cuits is Ohm’s law. This shows mathemati-
cally the relationship between voltage (E),
35
conductive
pathway
control
electrical circuit
load
Ohm’s law
voltage source
4
Ohm’s Law