In a circuit with a fixed voltage, if the resistance doubles, what happens to current and power?

• A. Current halves; power halves.
• B. Current doubles; power doubles.
• C. Current halves; power stays the same.
• D. Current stays the same; power halves.

Answer: (A)

With a fixed voltage, current follows I = V/R. If the resistance doubles, the current becomes I' = V/(2R) = I/2, so the current halves. Power with fixed voltage is P = VI, so if I halves, P also halves (P = V × I → P' = V × (I/2) = P/2). Alternatively, P = V^2/R shows P halves when R doubles. So both current and power halve.