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What makes work positive (electricity)

by Eats Dirt
Tags: potential energy, work done
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Eats Dirt
Feb28-12, 09:02 PM
P: 70
I dont really understand the concept of what makes work positive or negative for example if 3 charges are brought together from infinite what is the work done on them?

I am extremely confused about what make work positive and negative.
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Feb29-12, 05:20 AM
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Hi Eats Dirt!

Potential energy = minus the work done by a conservative force.

And work done = force "dot" displacement
so if the charge is attractive (like gravity), the force is in the same direction as displacement, so the work done by the force is positive, and the potential energy difference is negative

but if the charge is repulsive, the force is in the opposite direction to displacement, so the work done by the force is negative, and the potential energy difference is positive

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