terms like 'magnetostriction,' mu-metal,' and 'D-ring' arouse your
technostimulus receptors, then this quiz on magnetics should be
just what you've been waiting for. It appeared in a 1962 edition
of Popular electronics, but the principles therein have not changed
since then. I must admit that I had never given thought to the orientation
in which bar magnets should be stored when in close proximity to
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
See all articles from
Magnetic Phenomena Quiz
By Robert P. Balin
Neither magnets nor magnetism are mysteries
to the experimenter. But this quiz will test your knowledge of the
basic principles of magnetic phenomena. Mark each statement "True"
or "False" and check your answers at the bottom.
||1 - The north pole of a compass
points to the earth's north magnetic pole.
2 - If the separation
between two unlike magnetic poles is reduced by half, the
attraction between them will become four times as great.
3 - If a compass is placed beneath a wire
passing electrons from A to B, its north pole will point
to the right.
4 - Bar magnets should be stored
by placing them so that like poles are side by side.
5 - There is no insulator for
magnetic fields. Some metals simply offer more resistance
to magnetism than others.
||6 - A "D-ring" is usually found
on d.c. electromagnetic relay coils.
7 - When a nickel-iron
rod is magnetized, it will grow shorter in length.
8 - The electromagnet shown here
will have its north pole located at the top of the coil.
9 - An electron passing through
the deflection yoke magnetic field and out of the page will
be deflected to the right.
10 - A "keeper" is placed across
the poles of a horseshoe magnet to prevent the magnet's
field from passing through nearby ferrous objects.
Popular Electronics published many quizzes over the years - some
really simple and others not so simple. Robert Balin created many of the quizzes. This is
a listing of all I have posted thus far.
- Scope-Trace Quiz,
March 1965 Popular Electronics
Circuit Analogy Quiz, April 1973 Popular Electronics
- Test Your
Knowledge of Semiconductors, August 1972
- Ganged Switching Quiz,
- Lamp Brightness Quiz,
Lissajous Pattern Quiz, September 1963
Quizoo, October 1962
Photo Album Quiz, March 1963
Alphabet Quiz, May 1963
- Quiz: Resistive?
Inductive? or Capacitive?, October 1960
Vector-Circuit Matching Quiz, June 1970
Quiz, September 1961
- RC Circuit Quiz,
- Diode Quiz, July
Curves Quiz, February 1963
Electronic Numbers Quiz, December 1962
Conversion Quiz, April 1963
- Coil Function
Quiz, June 1962
- Electronic Analogy
Quiz, November 1961 Popular Electronics
- Electronic Coupling
Quiz, August 1973 Popular Electronics
Analogy Quiz, August 1960
- Audio Quiz,
Unit Quiz, May 1962
Circuit Quiz, June 1968
on AC Circuit Theory, December 1970
Magnetic Phenomena Quiz, February 1962
Electronics Geography Quiz, April 1970
Menu Quiz, August 1963
Noise Quiz, August 1962
Current Quiz, October 1963
- Electronic Inventors Quiz, November 1963
Function Quiz, January 1962
Measurement Quiz, January 1963
- Vacuum Tube
Quiz, February 1961
- Kool-Keeping Kwiz, June
1 TRUE. The north pole of a compass
points to the earth's north magnetic pole which is actually the
south pole of a large magnet inside the earth.
2 TRUE. The
force of attraction between unlike magnetic poles varies inversely
as the square of the distance between them.
3 TRUE. The
north pole of a compass always indicates the direction of the magnetic
field in which it lies. To determine the direction of the magnetic
field, grasp the wire with your left hand with the thumb in the
direction of electron flow, from A to B. Your fingertips will point
in the direction of the magnetic field.
4 FALSE. Bar magnets
should be stored so that opposite poles lie adjacent to each other.
The magnetic field from each bar will then have a closed magnetic
circuit lying entirely within the bars themselves. Hence, the magnetic
fields are least likely to go into nearby metallic objects.
5 TRUE. There are no materials which resist magnetic fields.
However, magnetic shields made of high-permeability materials such
as mu-metal are used to bypass magnetic fields around the devices
to be isolated from the effects of the magnetic fields.
6 FALSE. The D-ring is a shorted turn of copper used on a.c. relay
coils to prevent armature chattering. When the magnetic field set
up by the coil starts to collapse on alternate half cycles, a circulating
current in the D-ring builds up a magnetic field which holds the
7 TRUE. This is the principle of "magnetostriction"
used in ultrasonic transducers for sonar and in ultrasonic cleaning
8 TRUE. Electrons will enter the coil from the
bottom and exit at the top of the coil. Grasp the coil with your
left hand with the fingers wrapped in the direction of the electron
flow. Your thumb will point to the north pole.
Use your left hand to determine the magnetic field around a moving
electron. The thumb points in the direction of electron flow and
the curled fingers point in the direction of its magnetic field.
Hence, the electron coming out of the page will have a clockwise
field around it. The magnetic field to the right of the electron
will have the same direction as the field of the deflection coil.
Since magnetic lines which have the same direction repel each other,
the electron experiences a force to the left.
10 TRUE. Almost
all of the magnet's magnetic lines of force will pass through the
soft iron bar. The "keeper" is usually employed when storing permanent
magnets in order to preserve the magnetic strength.
Posted June 12, 2013