If the length of a wire doubles, keeping material and cross-sectional area constant, the resistance will

• A. Double.
• B. Remain the same.
• C. Halve.
• D. Increase by a factor of four.

Answer: (A)

Resistance in a uniform wire scales with its length when the material and cross-sectional area stay the same. The relationship R = ρL/A shows this clearly: if you double the length L while ρ and A are unchanged, the resistance doubles. The intuition is simple—electrons have to travel a longer path, colliding with atoms more often, which makes it harder for current to flow. If the length didn’t change, or if the area increased, the resistance would stay the same or decrease accordingly; doubling the length specifically increases resistance once length changes while other factors are held constant.