Page 39 - Teach Yourself Electricity and Electronics

Quiz 19

generator works. Generators can also work backwards. Then you have a motor that
changes electricity into useful mechanical energy.
A magnetic field contains energy of a unique kind. The science of magnetism is
closely related to electricity. Magnetic phenomena are of great significance in electron-
ics. The oldest and most universal source of magnetism is the flux field surrounding the
earth, caused by alignment of iron atoms in the core of the planet.
A changing magnetic field creates a fluctuating electric field, and a fluctuating
electric field produces a changing magnetic field. This phenomenon, called electro-
magnetism, makes it possible to send radio signals over long distances. The electric
and magnetic fields keep producing one another over and over again through space.
Chemical energy is converted into electricity in all dry cells, wet cells, and bat-
teries. Your car battery is an excellent example. The acid reacts with the metal elec-
trodes to generate an electromotive force. When the two poles of the batteries are
connected, current results. The chemical reaction continues, keeping the current
going for awhile. But the battery can only store a certain amount of chemical energy.
Then it “runs out of juice,” and the supply of chemical energy must be restored by
charging. Some cells and batteries, such as lead-acid car batteries, can be recharged
by driving current through them, and others, such as most flashlight and
transistor-radio batteries, cannot.

Quiz

Refer to the text in this chapter if necessary. A good score is at least 18 correct answers
out of these 20 questions. The answers are listed in the back of this book.
1. The atomic number of an element is determined by:
A. The number of neutrons.
B. The number of protons.
C. The number of neutrons plus the number of protons.
D. The number of electrons.
2. The atomic weight of an element is approximately determined by:
A. The number of neutrons.
B. The number of protons.
C. The number of neutrons plus the number of protons.
D. The number of electrons.
3. Suppose there is an atom of oxygen, containing eight protons and eight
neutrons in the nucleus, and two neutrons are added to the nucleus. The resulting
atomic weight is about:
A. 8.
B. 10.
C. 16.
D. 18.