Electromagnetism and Magnetic Circuits - Quiz
Electrician's Mate 3 - Navy Training Courses
Chapter 3 - NAVPERS 10548

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 out. See copyright. See Table of Contents.

- U.S. Government Printing Office; 1949

CHAPTER 3 QUIZ

ELECTROMAGNETISM AND MAGNETIC CIRCUITS

** See the important note about conventional 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 electric current?

3. If you reverse the current in a wire how does that change the field around the wire?

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 them.

      (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 the core.

       (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:
       (a) The 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 of turns.

          (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 the .

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 the reluctance.

         (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 carrying conductor

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

8. Solenoid

9. At the center

10. Field, current

11. (a) flux (b) attracted

12. 1. Magnetic brake; 2. magnetically operated circuit breakers; 3 solenoid-operated valves

13. (a) electromagnet (b) circuit

14. (a) flux (b) greater (c) greater (d) 1. increase 2. increase (e) ampere-turns (f) gilbert

15. reluctance

16. permeability

17. (a) directly (b) inversely (c) magnetomotive force reluctance

18. (a) saturation (b) retentivity (c) hysteresis (d) heat