Three points charges of `1 C, 2C and 3C` are placed at the corners of an equilateral triangle of side 100 cm. Find the work done to move these charges to the corners of a similar equilateral triangle of side 50 cm.

Explanation

`U_(1) = (1)/(4 pi in_(0)) . [(Q.2Q)/(d) + (2Q . 3Q)/(d) + (3Q.Q)/(d)]`
`= (1)/(4 pi in_(0)) .(11 Q^(2))/(d)`
`U_(2) = (1)/(4 pi in_(0)) . [(Q . 2Q)/(d//2) + (2Q.3Q)/(d//2) + (3Q.Q)/(d//2)]`
`= (1)/(4 pi in_(0)) .(22 Q^(2))/(d)`
`W_(1 rArr 2) = U_(2) - U_(1) = (1)/(4 pi in_(0)) .(11 Q^(2))/(d)`