Key Topic 13: Power Relationships

Question 1

3-13B1: what does the power factor equal in an R-L circuit having a 60 degree phase angle between the voltage and the current?

A. 0.414
B. 0.866
C. 0.5
D. 1.73

Answer 1

C. 0.5

Question 2

3-13B2: If a resistance to which a constant voltage is applied is halved, what power dissipation will result?

A. Double.
B. Halved.
C. Quadruple.
D. Remain the same.

Answer 2

A. Double.

Question 3

3-13B3: 746 watts, corresponding to the lifting of 550 pounds at the rate of one-foot-per-second, is the equivalent of how much horsepower?

A. One-quarter horsepower.
B. One-half horsepower.
C. Three-quarters horsepower.
D. One horsepower.

Answer 3

D. One horsepower.

Question 4

3-13B4: In a circuit where the AC voltage and current are out of phase, how can the true power be determined?

A. By multiplying the apparent power times the power factor.
B. By subtracting the apparent power from the power factor.
C. By dividing the apparent power by the power factor.
D. By multiplying the RMS voltage times the RMS current.

Answer 4

A. By multiplying the apparent power times the power factor.

Question 5

3-13B5: What does the power factor equal in an R-L circuit having a 45 degree phase angle between the voltage and the current?

A. 0.866
B. 1.0
C. 0.5
D. 0.707

Answer 5

D. 0.707

Question 6

3-13B6: What does the power factor equal in an R-L circuit having a 30 degree phase angle between the voltage and the current?

A. 1.73
B. 0.866
C. 0.5
D. 0.577

Answer 6

B. 0.866