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Chapter 11 Electrical Engineering 225
See Workbook Activity 11-2 to learn how
make a simple cell that will produce electricity.
Solar Cells
Solar cells use light to create electricity. Inside
a solar cell, a layer of positive semiconductor mate-
rial is sandwiched together with a layer of negative
semiconductor material. Semiconductors, such as
silicon, have conductive properties between those of
conductors and insulators. When light shines on the
cell, some of the light energy is absorbed. This energy
knocks electrons loose, and they begin to fl ow in the
form of electrical current. Many small cells can be
connected to power devices like calculators, satel-
lites, and even entire houses. See Figure 11-8.
See Workbook Activity 11-3 to use solar cells
to power a lightbulb.
Characteristics and Measurements
Once electricity is generated, it has certain
characteristics that electrical engineers use in a
number of different ways. It is important for elec-
trical engineers to understand these characteris-
tics and how to measure them.
Voltage
Voltage is the amount of pressure causing
the fl ow of electrons, which is expressed as elec-
tromotive force (EMF). Voltage is also known
as potential difference because it describes the
difference in charge from one place to the other. A
higher voltage will cause more electrons to fl ow.
The letter E is often used as an abbreviation for
voltage and stands for electromotive force. Volt-
age is measured in volts. The abbreviation for
volts is the letter V. Typical wall outlets in a house
provide 120 V, while a battery used to power a
fl ashlight might provide 1.5 V.
Current
Current is a measure of the fl ow of electrons
per unit time. To understand current, you must
fi rst understand coulombs, which is a measure of
the amount of electricity. One coulomb is equal
to 6.24 × 1018 electrons. The term amperage is also
used to describe current.
When discussing the fl ow of electrons, it
is important to include time. As an example,
let’s say 100 students walked down the hall
in front of your classroom. That doesn’t mean
much to you unless you know the time frame.
Did it take all day for 100 students to pass by?
Would it mean more if it were 100 students in
two minutes?
One ampere, or amp, is the measurement
of one coulomb of charge passing a point in one
second. The letter I is used as an abbreviation for
current because it stands for intensity. Current
is measured in amps. The letter A is used as an
abbreviation for amps. For example, a common
100-watt lightbulb draws about 0.83 amps.
Polarity refers to the positive or negative
condition at the power supply terminal. Some-
times polarity is constant and current fl ows in only
one direction. This is called direct current (dc).
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Figure 11-8. 
Solar cells can be used to power several different types of
devices, such as this navigational buoy.