Question

A metallic sphere has a charge of 10 µC. A unit negative charge is brought from A to B both 100 cm away from the sphere but A being east of it while B being on west. The net work done is
(a) Zero (b) 2/10 joule (c) –2/10 joule (d) –1/10 joule

Answer 1

Dear student
$$\begin{gathered} Workdone=changeinpotentialenergy \\ W=U_f-U_i \\ {U}_i=\frac{1}{4\pi \in }\frac{1\times 10\times {10}^{-6}}{1}(U_{i}istheinitialpotentialenergywhenunitchargeislyingeast) \\ {U}_f=\frac{1}{4\pi \in }\frac{1\times 10\times {10}^{-6}}{1}(U_{f}isthefinalpotentialenergywhenunitchargeislyingwest) \\ W=\frac{1}{4\pi \in }\frac{1\times 10\times {10}^{-6}}{1}-\frac{1}{4\pi \in }\frac{1\times 10\times {10}^{-6}}{1}=0 \\ W=0 \\ Regards \end{gathered}$$