Exams › JEE Advanced › Physics
When a positive charge is displaced against (opposite to) the direction of an electric field, which statement is true?
- the potential energy of the system decreases
- energy must be supplied by an external agent
- the field performs positive work on the charge
- the strength of the field decreases
Correct answer: energy must be supplied by an external agent
Solution
The electric force on a positive charge points along E. Displacing the charge opposite to E means the displacement is against the force, so the field does negative work. By work-energy considerations, an external agent must supply energy, increasing the potential energy of the system. The field strength itself is unaffected by moving a test charge.
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