Work done in moving a unit positive charge in space by an external force

1. Aug 7, 2010

Ashu2912

Consider a positive charge +q placed at the origin. Let A and b be two points in the space with position vectors rA and rB respectively. What will be the work done by an external force equal and opposite to the Coulumbic force, in moving a unit positive charge from A to B, irrespctive of the path AB???

I have derived it as W = kq ((1/rA) - (1/rB)), but my book tells that W = kq ((1/rB) - (1/rA)), where k = electrostatic constant. Please help me!!!!!!

2. Aug 7, 2010

zhermes

Settle down tiger :p
The work done, is the change in energy
$$W = \Delta E = E_{final} - E_{initial}$$
You're just off by a minus sign.

3. Aug 8, 2010

Ashu2912

Can you get me the derivation????

4. Aug 8, 2010

rock.freak667

You already did the derivation, you are just off by a minus sign.

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