Suppose the filament length is doubled to 1.20 m while the potential difference remains 120 V and the diameter remains constant. What is the electric field strength inside the filament?

• A. 100 V/m
• B. 200 V/m
• C. 50 V/m
• D. 400 V/m

Answer: (A)

When a potential difference is applied across a conductor, the electric field inside is the potential gradient along its length, E ≈ V/L for a uniform drop. Doubling the length while keeping the same voltage reduces the gradient in half. The diameter doesn’t change this gradient in this simple view, since the field depends on how much voltage per unit length is applied.

Compute the field: E = V/L = 120 V / 1.20 m = 100 V/m.