Which configuration requires the most electrical power?

Which configuration requires the most electrical power?

• A. Four 30 watt lamps arranged in a 12 volt parallel circuit
• B. A 24 volt anticollision light circuit consisting of 2 light assemblies which require 3 amperes each during operation
• C. A 100 watt load at 5 volts
• D. A 1/5 HP 24 volt motor which is 75 percent efficient

Answer: (D)

Power is the rate of energy use, given by P = VI. When a device has a stated mechanical output and efficiency, the electrical input is P_in = P_out / η. Four 30-watt lamps at 12 V: each lamp uses 30 W, so total is 4 × 30 = 120 W. Two 24 V light assemblies drawing 3 A each: total current is 6 A, so P = 24 V × 6 A = 144 W. A 100-watt load at 5 V already specifies its electrical power, so it uses 100 W. A 1/5 HP (0.2 HP) motor at 24 V with 75% efficiency: 0.2 HP ≈ 0.2 × 746 ≈ 149 W of mechanical output. Input power is 149 W / 0.75 ≈ 199 W. Thus, the motor configuration requires the most electrical power (about 199 W).

Power is the rate of energy use, given by P = VI. When a device has a stated mechanical output and efficiency, the electrical input is P_in = P_out / η.

Four 30-watt lamps at 12 V: each lamp uses 30 W, so total is 4 × 30 = 120 W.

Two 24 V light assemblies drawing 3 A each: total current is 6 A, so P = 24 V × 6 A = 144 W.

A 100-watt load at 5 V already specifies its electrical power, so it uses 100 W.

A 1/5 HP (0.2 HP) motor at 24 V with 75% efficiency: 0.2 HP ≈ 0.2 × 746 ≈ 149 W of mechanical output. Input power is 149 W / 0.75 ≈ 199 W.

Thus, the motor configuration requires the most electrical power (about 199 W).