What is the standard equation that relates power, current, and voltage?

What is the standard equation that relates power, current, and voltage?

• A. P = IV
• B. P = I^2 R
• C. P = V^2 / R
• D. P = V / I

Answer: (A)

Power in an electrical circuit is the rate at which energy is transferred, and it equals the product of voltage and current: P = IV. Voltage tells us how much energy per unit charge is available, and current tells us how many charges pass per unit time. Multiply them, and you get energy transferred per unit time, i.e., power, measured in watts. If you know the resistance, you can use Ohm’s law to rewrite the same relationship in different forms. With V = IR, substituting into P = IV gives P = V^2 / R. With I = V / R, substituting into P = VI gives P = I^2 R. These are just alternate ways to express the same power when the circuit includes a resistor. Example: across a 12 V source drawing 3 A, P = IV = 12 × 3 = 36 W. If that same circuit has a 4 Ω resistor, the current is I = V/R = 12/4 = 3 A, and P = V^2/R = 144/4 = 36 W, or P = I^2R = 9 × 4 = 36 W.

Power in an electrical circuit is the rate at which energy is transferred, and it equals the product of voltage and current: P = IV. Voltage tells us how much energy per unit charge is available, and current tells us how many charges pass per unit time. Multiply them, and you get energy transferred per unit time, i.e., power, measured in watts.

If you know the resistance, you can use Ohm’s law to rewrite the same relationship in different forms. With V = IR, substituting into P = IV gives P = V^2 / R. With I = V / R, substituting into P = VI gives P = I^2 R. These are just alternate ways to express the same power when the circuit includes a resistor.

Example: across a 12 V source drawing 3 A, P = IV = 12 × 3 = 36 W. If that same circuit has a 4 Ω resistor, the current is I = V/R = 12/4 = 3 A, and P = V^2/R = 144/4 = 36 W, or P = I^2R = 9 × 4 = 36 W.