When a charge moves through an electric circuit in the direction of an electric force, it

Analyze the question: A charge moves in the same direction as the electric force acting on it. We need to decide what happens to its potential and kinetic energy.

Concept: The electric force does positive work on the charge when the charge moves along the direction of the force.

• By the work-energy theorem, positive work done on the charge increases its kinetic energy.
• The electric field is a conservative field, so energy is conserved. If kinetic energy goes up, electric potential energy must go down.

This is like a ball falling under gravity. The ball moves in the direction of the gravitational force, so it loses gravitational potential energy and gains kinetic energy.

Solution:

1. The force and the displacement are in the same direction, so W = Fd cos 0° = Fd, which is positive.
2. Positive work means the kinetic energy increases (ΔKE > 0).
3. For a conservative force, ΔPE = −W, so ΔPE < 0. The potential energy decreases.
4. The charge therefore loses potential energy and gains kinetic energy.

Checking the options:

• A: Both cannot increase, since that would violate energy conservation.
• B: This is the reverse of what happens. It describes moving against the force.
• C: Correct.
• D: Both cannot decrease without some other energy loss.

**Answer: C.

Exam tip: Remember "with the force, PE falls and KE rises" (like a falling stone). If you move against the force, you must do work, so PE rises.