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An external agent brings a charge of -5 C from infinity to a certain point in an electrostatic field, doing 100 J of work in the process. What is the electric potential at that point?
- +10 V
- -10 V
- +20 V
- -20 V
Correct answer: -20 V
Solution
Since W_ext = q*V (with V at infinity zero), dividing 100 J by the charge -5 C gives -20 V. The negative charge requiring positive external work means it is being pushed toward a region of negative potential.
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