Key Topic 21: Transformers

Question 1

3-21C1: A capacitor is sometimes placed in series with the primary of a power transformer to:

A. Improve the power factor.
B. Improve output voltage regulation.
C. Rectify the primary windings.
D. None of these.

Answer 1

A. Improve the power factor.

Question 2

3-21C2: A transformer used to step up its input voltage must have:

A. More turns of wire on its primary than on its secondary.
B. More turns of wire on its secondary than on its primary.
C. Equal number of primary and secondary turns of wire.
D. None of the above statements are correct.

Answer 2

B. More turns of wire on its secondary than on its primary.

Question 3

3-21C3: A transformer primary of 2250 turns connected to 120 VAC will develop what voltage across a 500-turn secondary?

A. 26.7 volts.
B. 2300 volts.
C. 1500 volts.
D. 5.9 volts.

Answer 3

A. 26.7 volts.

Question 4

3-21C4: What is the ratio of the output frequency to the input frequency of a single-phase full-wave rectifier?

A. 1:1
B. 1:2
C. 2:1
D. None of these.

Answer 4

C. 2:1

Question 5

3-21C5: A power transformer has a single primary winding and three secondary windings producing 5.0 volts, 12.6 volts, and 150 volts. Assuming similar wire sizes, which of the three secondary windings will have the highest measured DC resistance?

A. The 12.6 volt winding.
B. The 150 volt winding.
C. the 5.0 volt winding.
D. All will have equal resistance values.

Answer 5

B. The 150 volt winding.

Question 6

3-21C6: A power transformer has a primary winding of 200 turns of #24 wire and a secondary winding consisting of 500 turns of the same size wire. When 20 volts are applied to the primary winding, the expected secondary voltage will be:

A. 500 volts.
B. 25 volts.
C. 10 volts.
D. 50 volts.

Answer 6

D. 50 volts.