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A spherical shell of radius R(1) with un...

A spherical shell of radius `R_(1)` with uniform charge q is expanded to a radius `R_(2)`. Find the work performed by the electric forces in this process.

Text Solution

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Initial self - energy
`U_i = (q^2)/(8 pi epsilon_0 R_1)`
final self - energy
`U_f = (q^2)/(8 pi epsilon_0 R_2)`
`Delta U = U_f - U_i = (q^2)/(8 pi epsilon_0) ((1)/R_(2) - (1)/R_(1))`
Work done by electrical forces is
`W = - Delta U = (q^2)/(8 pi epsilon_0) [(1)/R_(2) - (1)/R_(1)]`.
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