If resistance is doubled, what happens to the current?

• A. It is reduced to one-half.
• B. It increases to two times.
• C. It remains the same.
• D. It increases by half.

Answer: (A)

With a constant voltage source, current through a resistor follows I = V/R. Doubling the resistance makes the denominator twice as large, so I becomes (V)/(2R), which is half of the original current. So the current is reduced to one-half. If the voltage weren’t fixed, other outcomes could happen, but under a fixed voltage, doubling resistance always halves the current.