General - AM.I.A.K12 - Power

Question 1

What is the formula for power in a DC circuit?

Answer 1

Power = voltage x current
P = E x I

Question 2

What is the relationship between mechanical and electrical power?

Answer 2

1 horsepower = 746 watts

Question 3

What is meant by true power in an AC circuit?

Answer 3

The product of the circuit voltage and the current that is in phase with this voltage

Question 4

In what units is true power expressed?

Answer 4

Watts

Question 5

What is meant by apparent power in an AC circuit?

Answer 5

• The product of the circuit voltage and the circuit current
• without reference to phase angle

Question 6

In what units is apparent power expressed?

Answer 6

Volt-amps

Question 7

What is meant by reactive power in an AC circuit?

Answer 7

• The power consumed in the inductive and capacitive reactances in an AC circuit
• Reactive power is also called wattless power

Question 8

In what units is reactive power expressed?

Answer 8

In volt-amps reactive (VAR) or kilovolt-amps reactive (KVAR)

Question 9

What is meant by power factor in an AC circuit?

Answer 9

-The ratio of true power to apparent power
- true power:apparent power
- It is also the ratio of circuit resistance to circuit impedance

Question 10

How many watts of power are consumed by a 1/5 horsepower, 24-volt DC motor that is 75% efficient?

Answer 10

Power efficiency is expressed as:

Efficiency = power out/power in

Power consumed is the same as power in, and 1 horsepower (hp) equals 746 watts

Power in = power out/efficiency = 1/5 (hp) x 746 (watts) / 0.75

= 0.2 x 746 / 0.75 = 199 watts