Magnetic Phenomena Quiz
February1962 Popular Electronics
If 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 each other.
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
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
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
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.
See answers below.
Popular Electronics published many quizzes over the years
- some really simple and others not so simple. Robert P. Balin created many of the quizzes.
This is a listing of all I have posted thus far.
- A Baffling Quiz
- January 1968
- Electronics IQ Quiz
- May 1967
- Plug and Jack Quiz
- December 1967
Switching Quiz - October 1967
Angle Quiz - September 1967
Electronics Quiz - July 1967
- Bridge Circuit
Quiz -December 1966
- Diode Function
Quiz - August 1965
- Diagram Quiz, August
- TV Trouble Quiz,
- Electronics History Quiz,
- Scope-Trace Quiz,
Circuit Analogy Quiz, April 1973
Your Knowledge of Semiconductors, August 1972
- Ganged Switching
Quiz, April 1972
- Lamp Brightness
Quiz, January 1969
- Lissajous Pattern Quiz, September 1963
Quizoo, October 1962
- Electronic Photo Album Quiz, March 1963
- Electronic Alphabet Quiz, May 1963
- Quiz: Resistive?
Inductive? or Capacitive?, October 1960
- Vector-Circuit Matching Quiz, June 1970
Quiz, September 1961
- RC Circuit
Quiz, June 1963
- Diode Quiz,
- Electronic Curves Quiz, February 1963
- Electronic Numbers Quiz, December 1962
- Energy Conversion Quiz, April 1963
Function Quiz, June 1962
Quiz Part I - February 1964
Quiz - February 1967
- Unknown Frequency
Quiz - September 1965
Metals Quiz - October 1964
Measurement Quiz - August 1967
- Meter-Reading Quiz,
Geometry Quiz, January 1965
Factor Quiz, November 1966
Math Quiz, November 1965
- Series Circuit Quiz,
Quiz, March 1966
- Electronic Analogy
Quiz, November 1961
Coupling Quiz, August 1973
- Electronics Analogy Quiz, August 1960
- Audio Quiz,
Unit Quiz, May 1962
Capacitor Circuit Quiz, June 1968
- Quiz on AC Circuit Theory, December 1970
- Magnetic Phenomena Quiz, February 1962
- Electronics Geography Quiz, April 1970
Electronic Menu Quiz, August 1963
- Electronic Noise Quiz, August 1962
- Electronic Current Quiz, October 1963
- Electronic Inventors Quiz, November 1963
Function Quiz, January 1962
- Electronic Measurement Quiz, January 1963
Tube Quiz, February 1961
- Kool-Keeping Kwiz, June
- Find the
Brightest Bulb Quiz, April 1960
Magnetic Quiz Answers
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.
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.
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 contacts
7 TRUE. This is the principle of "magnetostriction" used in ultrasonic
transducers for sonar and in ultrasonic cleaning devices.
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.
9 FALSE. 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