Mr. Smith did 20 J of work in bringing a +2C charge slowly from infinity to a point A against the electrostatic field of a point charge +Q fixed at the origin. If we now define the potential energy per unit charge at point A to be W J/C considering B(5,0) as the reference point. The work done by Smith in taking the same charge from B to A is?

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20 J

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None of these

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Solution

The correct option is B 2W
If you read the question carefully you’ll find that the first sentence is irrelevant information. The potential energy at A is defined as W J/C with respect to B. Thus the work done to bring 1C charge from B to A is W. So to bring 2C charge from B to A, work done is obviously 2W.

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