6 September 2015
QI am in the sixth grade and am working on a project for school about how radios work. Can you help me by explaining how the radio signals can be received through the air?
ASixth grade is a great time to start learning about one of the most fascinating technologies of our times. Radio signals are traveling electromagnetic waves which can move
through air or even the relatively empty reaches of
outer space (Figure 1). Radio waves are used to carry
information (such as music, voice, telephone, computer
data) from a sender (a.k.a., transmitter) to a receiver.
The theory behind radio stretches back to the Persians
who developed batteries by using an iron rod and copper
cylinder in a clay jar with some acid material to produce
low voltages as shown in Figure 2 (you can do the same
thing in a cup using a steel plate, a copper plate, and
lemon juice). Unfortunately, the Persians had no use for
these batteries since the electric light bulb, MP3 players,
and TV would not be invented for several thousand years.
The Greeks discovered static electricity (what makes
your hair stand up when you slide down a plastic board)
by rubbing fur on a piece of tree resin called amber. I
like the static charge
which causes the plastic
wrapper to jump back
out of the trash can and
attach itself to your hand.
discovered that lightning
was a moving stream of
electrical particles. These
discoveries were neat,
but had no practical use.
In the 1600s through
the 1800s, scientists
discovered many more
things about electricity.
Some of these discoveries were useful, and eventually lead
to the development of radios. Charles Coulomb discovered
like charges repel and unlike charges attract (Figure 3).
The positive charges were atoms missing negative charges,
which were named electrons (Figure 4). Michael Faraday
discovered that if you move a magnet through a coil
of wire or vice versa, you can generate a voltage (the
principle of the electric generator) as shown in Figure 5.
Voltage pushes electrons through a wire just like
pressure from a pump pushes water through a pipe (Figure
6). The moving stream of electrons is called current;
the wire tries to keep the electrons from flowing by its
Georg Ohm (yes,
this is the correct
spelling) discovered that
the current through a
wire (I) is equal to the
voltage between the
ends of the wire (V) and
the wire’s resistance
(R). As a formula, this is
represented as I = V/R,
or what we call Ohm’s
n WITH TIM BROWN Q & A
In this column, Tim answers questions about
all aspects of electronics, including computer hardware, software, circuits, electronic
theory, troubleshooting, and anything else of
interest to the hobbyist. Feel free to participate with your questions, comments, or suggestions. Send all questions and comments
• Explanation of Radio Propagation
• Troubleshooting Tips
n FIGURE 1
n FIGURE 2
n FIGURE 3
n FIGURE 4