Question

A charge of +10 C is fixed at the origin. Choosing the reference point at A(1,2), the change in potential energy of the system when a charge of +1C is taken from A to infinity is?

• A. Positive
• B. Negative
• C. Zero
• D. None of these

Answer 1

The correct option is B Negative

Now recall that the change in potential energy of the system is positive when positive work is done by external agent against the conservative electrostatic field as the configuration of the system changes.
Now if infinity is taken as reference point, then work done by external agent in taking a charge from infinity to the point A would have been positive. But here the reference point is A, which implies potential energy of system is assumed to be zero when +1C is at A.So when taken to infinity from A, work done by field of +10 C will be positive and by an external agent will be negative.
Therefore change in potential energy will be negative.