DC Theory Lesson 5

Current flowing through a conductor develops a magnetic field flux of concentric circles expanding (perpendicular) outward from the conductor.

Select one:

True

False

If a student uses his or her left hand and points the thumb in the direction of current flow, the encircling fingers will give the direction of the magnetic field, when applying the left hand rule.

Select one:

True

False

If a person knows the direction of current flow in a conductor, how can he or she determine the direction of flux lines?

a. By applying Thevenin's Theorem

b. By the amount of resistance in the conductors

c. By using Kirchhoff's Law

d. By using the left hand rule for conductors

The strength of an electromagnetic field can be increased by increasing the ? conductor.

a. current flowing through the

b. resistance of the

c. voltage through the

d. any of the above

Which of the following current-carrying conductors show opposing magnetic fields?

a. a. only

b. a. and b.

c. b. only

d. a. and c.

e. c. only

f. a., b., and c.

When a current carrying conductor is wound in a coil, a magnetic field is produced that will have a north and south pole.

Select one:

True

False

Increasing the number of loops will increase the ? of the magnetic field.

a. current

b. resistance

c. size

d. strength

What measurement is used to denote the magnetic field strength of a coil or electromagnet?

a. ampere-turns

b. relative motion

c. resistance

d. turns comparison

Wrapping the windings closer together will create a(n) ? magnetic field.

a. larger

b. smaller

c. stronger

d. tighter

Adding a core of ferromagnetic material to the coil decreases the number of flux lines passing through the center of the coil, thereby decreasing the strength of the magnet.

Select one:

True

False

When a core is ? , there is no longer a change in the strength of the magnetic field when current through the coil is increased.

a. de-magnetized

b. energized

c. saturated

d. none of the above

A concept of electromagnets is that it takes energy to maintain a magnet, but does not take energy to make a magnet.

Select one:

True

False

Which of the following best describes why soft iron is used for the core of an electromagnet?

a. Soft iron has low reluctance.

b. Soft iron is magnetic.

c. Soft iron will not become permanently magnetized.

d. b. and c.

e. a., b., and c.

How can the north and south poles of a coil or electromagnet be determined?

a. Using Ohm's Law

b. Using Norton's Theorem

c. Using the left hand rule for coils

d. Using the right hand rule for coils

The electrons move in a conductor because of the interaction between the magnetic field of the magnet and the magnetic field of the electrons. This motion causes a voltage to be induced in the conductor.

Select one:

True

False

Changing the direction of the conductor passing through the flux lines will change the ? .

a. amount of resistance in the circuit

b. amount of voltage at the source

c. direction of the current flow

d. all of the above

In order for a magnetic field to induce a voltage into a conductor, there must be ? between the two.

a. a ground connection

b. magnetic resistance

c. relative motion

d. resistance

If a conductor is moving parallel with the flux lines, ? volts will be induced.

a. 0

b. 0.5

c. 1.3

d. 2.5