18) Potential energy of a system comprising of point charges U1. When  a charge q  is added in the system without disturbing other charges, the potential energy becomes U2. The potential of the point where the charge q is placed in the system is.

( A )   U 2 - U 1 q ( B )   U 1 - U 2 q ( C )   U 1 + U 2 2 q ( D )   U 2 - U 1 2 q

Dear student
Let us consider two charges q1 and q2 in the system and the third charge is bought into the system from infinity.U1=14πq1q2r1 (r1 is separation between q1 and q2)when charge q3 is bought into the systemU2=14πq1q2r1+14πq2qr2+14πq1qr3U2=U1+q(14πq2r2+14πq1r3)=U1+q×VV=U2-U1qRegards

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