Which formula correctly expresses power in a resistor when voltage is known?

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Prepare for the CWEA Electrical/Instrumentation (E/I) Grade 1 Test. Use flashcards and multiple-choice questions, each with hints and explanations. Get ready for your exam!

Multiple Choice

Which formula correctly expresses power in a resistor when voltage is known?

Explanation:
Power in a resistor comes from the current drawn by the voltage across it. Start with P = VI. For a resistor, current is I = V/R, so substitute: P = V × (V/R) = V^2/R. That’s why the correct expression is P = V^2 / R when voltage is known. The other forms don’t match how voltage, current, and resistance relate and yield incorrect units (they wouldn’t give power in watts).

Power in a resistor comes from the current drawn by the voltage across it. Start with P = VI. For a resistor, current is I = V/R, so substitute: P = V × (V/R) = V^2/R. That’s why the correct expression is P = V^2 / R when voltage is known. The other forms don’t match how voltage, current, and resistance relate and yield incorrect units (they wouldn’t give power in watts).

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