What is the power dissipated in the 3 Ω resistor when connected to a 9 V source?

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Get ready for the NCCER Introduction to Electrical Circuits exam. Study with multiple choice questions, each question comes with hints and explanations. Ace your exam with confidence!

Multiple Choice

What is the power dissipated in the 3 Ω resistor when connected to a 9 V source?

Explanation:
Power dissipated by a resistor depends on the voltage across it, the current through it, and its resistance. For a resistor, Ohm’s law says I = V/R, so with 9 volts across 3 ohms the current is I = 9/3 = 3 amperes. The power is then P = V × I = 9 × 3 = 27 watts. You can also use P = V^2 / R = 9^2 / 3 = 81 / 3 = 27 watts, or P = I^2R = 3^2 × 3 = 9 × 3 = 27 watts. So the resistor dissipates 27 watts of power as heat.

Power dissipated by a resistor depends on the voltage across it, the current through it, and its resistance. For a resistor, Ohm’s law says I = V/R, so with 9 volts across 3 ohms the current is I = 9/3 = 3 amperes. The power is then P = V × I = 9 × 3 = 27 watts. You can also use P = V^2 / R = 9^2 / 3 = 81 / 3 = 27 watts, or P = I^2R = 3^2 × 3 = 9 × 3 = 27 watts. So the resistor dissipates 27 watts of power as heat.

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