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A positive charge is let go from rest in a uniform electric field. What happens to its electric potential energy?

1. It decreases because the charge moves along the direction of the electric field.
2. It stays constant because the field is uniform.
3. It increases because the charge moves along the field.
4. It decreases because the charge moves opposite to the field.

Correct answer: It decreases because the charge moves along the direction of the electric field.

Solution

The force on a positive charge is along E, so the released charge moves in the direction of the field. The field does positive work, increasing kinetic energy and therefore decreasing the electric potential energy. Energy is conserved (KE gained = PE lost).

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