Which formula should be used to calculate wattage for a resistor when its resistance and current are known?

Which formula should be used to calculate wattage for a resistor when its resistance and current are known?

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

Answer: (A)

Power dissipated by a resistor relates to current and resistance through P = I^2 R. This comes from starting with P = I V and then substituting V = I R, giving P = I (I R) = I^2 R. Since you know the current and the resistance, this form uses those values directly to yield the wattage. The other formulas require voltage (P = I V or P = V^2 / R), or aren’t standard for power in this context, so they’re less straightforward here.

Power dissipated by a resistor relates to current and resistance through P = I^2 R. This comes from starting with P = I V and then substituting V = I R, giving P = I (I R) = I^2 R. Since you know the current and the resistance, this form uses those values directly to yield the wattage. The other formulas require voltage (P = I V or P = V^2 / R), or aren’t standard for power in this context, so they’re less straightforward here.