Using P = I^2 × R, what is the power for a circuit with I = 3 A and R = 4 Ω?

Using P = I^2 × R, what is the power for a circuit with I = 3 A and R = 4 Ω?

• A. 12 W
• B. 24 W
• C. 36 W
• D. 48 W

Answer: (C)

Power in a resistor is given by P = I^2 R, showing how heat (power) depends on the current and the resistance. With I = 3 A and R = 4 Ω, square the current first: 3^2 = 9. Then multiply by the resistance: 9 × 4 = 36. So the circuit dissipates 36 watts. The units work out as A^2·Ω, which equals watts, confirming the result. This illustrates why using P = I^2 R is the straightforward way to find power in a purely resistive path.

Power in a resistor is given by P = I^2 R, showing how heat (power) depends on the current and the resistance. With I = 3 A and R = 4 Ω, square the current first: 3^2 = 9. Then multiply by the resistance: 9 × 4 = 36. So the circuit dissipates 36 watts. The units work out as A^2·Ω, which equals watts, confirming the result. This illustrates why using P = I^2 R is the straightforward way to find power in a purely resistive path.