The power dissipated by a resistor can be calculated as

• A. Product of current and impedance
• B. Current squared times resistance
• C. Voltage divided by resistance
• D. Resistance times voltage

Answer: (B)

Power dissipated in a resistor is given by P = I^2 R. This comes from combining Ohm’s law, V = IR, with the definition of electrical power, P = VI. Substituting V with IR into P = VI gives P = I(IR) = I^2 R. So the heating (power) depends on both the current through the resistor and its resistance.

The other expressions don’t represent power in a resistor. I times Z would yield a voltage-like quantity, not power, since Z is impedance and power uses voltage times current. V divided by R simplifies to the current, not power. R times V isn’t the correct form for power either; using V = IR would make that equal to I R^2, which isn’t power. Since P = I^2 R is the correct relationship, option B is the right choice.