How is power factor defined?

How is power factor defined?

• A. Real power divided by apparent power
• B. Apparent power divided by real power
• C. Real power times voltage
• D. Voltage divided by current

Answer: (A)

Power factor is a measure of how effectively electrical power is converted into useful work. It is defined as the ratio of real power to apparent power. Real power, in watts, is the actual energy per unit time used to do real work. Apparent power, in volt-amperes, combines the effect of voltage and current and includes both the useful power and the reactive power circulating in the system. The real-to-apparent power ratio yields a value between 0 and 1 (often expressed as a percentage) that shows how much of the supplied power is doing productive work. So the correct definition is real power divided by apparent power. The other options don’t describe this efficiency ratio: multiplying real power by voltage isn’t a ratio and doesn’t give a dimensionless power factor; voltage divided by current is impedance, not power factor; apparent power divided by real power would be the reciprocal of the power factor, not the definition.

Power factor is a measure of how effectively electrical power is converted into useful work. It is defined as the ratio of real power to apparent power. Real power, in watts, is the actual energy per unit time used to do real work. Apparent power, in volt-amperes, combines the effect of voltage and current and includes both the useful power and the reactive power circulating in the system. The real-to-apparent power ratio yields a value between 0 and 1 (often expressed as a percentage) that shows how much of the supplied power is doing productive work.

So the correct definition is real power divided by apparent power. The other options don’t describe this efficiency ratio: multiplying real power by voltage isn’t a ratio and doesn’t give a dimensionless power factor; voltage divided by current is impedance, not power factor; apparent power divided by real power would be the reciprocal of the power factor, not the definition.