Here is the "Electrician's Mate 3 - Navy Training Courses" (NAVPERS 10548)
in its entirety (or will be eventually). It should provide one of the Internet's best
resources for people seeking a basic electricity course - complete with examples worked
- U.S. Government Printing Office; 1949
CHAPTER 3 QUIZ
ELECTROMAGNETISM AND MAGNETIC CIRCUITS
** See the important note about
current flow direction on the main page **
1. How did Oersted discover that a magnetic field exists around a wire carrying
an electric current?
2. What is the shape or pattern of a magnetic field around a wire carrying an
3. If you reverse the current in a wire how does that change the field around
4. Complete the following statements: The left hand rule for the field around
a conductor says: When the thumb points in the direction of _________ the fingers
point in the direction of _________.
5. How does the field around a conductor carrying current change with distance
from the conductor?
6. Complete the following statements:
(a) When two parallel conductors have currents
flowing in opposite directions, their magnetic fluxes _________ in the space between
(b) When two parallel conductors have currents
flowing in opposite directions, their magnetic fields produce a force of _________.
(c) When two parallel conductors carry currents
in the same direction their magnetic fluxes in the space between them _________.
(d) When two parallel conductors carry currents
flowing in the same directions, their magnetic fields produce a force of _________
between the conductors.
7. Into what shape would you bend a current-carrying wire so that it would produce
the same kind of a field as a bar magnet?
8. A current-carrying coil shaped to produce a magnetic field like the field
of a bar magnet is called a _________.
9. At what place about such a coil is the field strongest?
10. Complete the following statements: When a coil carrying current is grasped
in 'the left hand, so the thumb points in the direction of the _________, the fingers
point in the direction of the _________.
11. Complete the following statements:
(a) If an iron core is placed near
a current-carrying coil, the field of the coil will produce magnetic _________ in
(b) If an iron core is placed near a current-carrying
coil the core will be _________ by the coil.
12. Name three applications, in electrical gear, for the principle of a current-carrying
coil acting on an iron core.
13. Complete these statements:
current-carrying coil and iron core combination is called an _________-_________-_________.
(b) The closed-loop path followed by magnetic
lines is called a magnetic _________.
14. Complete the following statements:
(a) The greater the magnetomotive force,
the greater the _________ in a magnetic circuit.
(b) The greater the current in the coil
of an electromagnet, the the magnetomotive force.
(c) The greater the number at turns in the
coil of an electromagnet, the _________ the magnetomotive force.
(d) To increase the magnetic pull of a current
carrying coil you
(1) _________ the number
(2) _________ the current.
(e) The number of turns of wire in a coil
times the number of amperes flowing in it is called the _________ of the coil.
(f) The unit of magnetomotive force is called
15. Opposition to the flow of magnetic flux in a magnetic circuit is called _________.
16. The ratio of the ability of a material to conduct magnetic flux compared
to air as a flux conductor is called the material's _________.
17. Complete the following statements: Flux produced in a magnetic circuit is
(a) _________ proportional to
the magnetomotive force.
(b) _________ proportional to
(c) Ohm's law for a magnetic
circuit can be expressed by the equation Flux= _
18. Complete the following statements:
(a) The flux density at which
an increase in magnetomotive force will not produce much increase in flux is called
the _________ density.
(b) Ability of a material to
retain magnetic flux after the magnetic force is removed is called .
(c) Energy loss due to friction
between molecules when forced into alignment by a magnetic force is called _________.
(d) This energy loss produces
_________ in the magnetic material.
Chapter 3 Answers
ELECTROMAGNETISM AND MAGNETIC CIRCUITS
1. By observing the motion of a compass needle when brought near the current
2. Circular field concentric with the conductor
3. Reverses the field
4. Current, field
5. Decreases with distance from the conductor
6. (a) add (b) repulsion (c) cancel (d) attraction
7. Circular loop
9. At the center
10. Field, current
11. (a) flux (b) attracted
12. 1. Magnetic brake; 2. magnetically operated circuit breakers; 3 solenoid-operated
13. (a) electromagnet (b) circuit
14. (a) flux (b) greater (c) greater (d) 1. increase 2. increase (e) ampere-turns
17. (a) directly (b) inversely (c) magnetomotive force reluctance
18. (a) saturation (b) retentivity (c) hysteresis (d) heat