The electric potential at point `A` is `20 V` and at `B` is `-40 V`. Find the work done by an external and electrostatic force in moving an electron slowly from B to A.

Explanation

Here, the test charge is an electron,
i.e., `q_(0) = 1.6 xx 10^(-19)C`
`V_(A) = 20 V` and `V_(B) = -40 V`
Work done by external force `(W_(BA))_("external force") = q_(0)(V_(A) - V_(B))`
`= (-1.6 xx 10^(-19))[(20) - (-40)] = -9.6 xx 10^(-18)J`
Work done by electric force
`(W_(BA))_("electric force") = -(W_(BA))_("external force")`
`= - (-9.6 xx 10^(-18)) J = 9.6 xx 10^(-18)J`