Charges`-q , Q, and -q` are placed at an equal distance on a straight liner. If the total potential energy of the system of three charges is zero, then find the ratio `Q//q`.
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Answer

`1 : 4`

Explanation

If x si the distance between the charges as shown in Fig, then potential energy of the system of three charges is

`(k(-q)Q)/(x) + (kQ (-q))/(x) + (k (-q) (-q))/(2x) = 0`
`- (2kqQ)/(x) + (kq^(2))/(2x) = 0 or (kq^(2))/(2x) = (2 kqQ)/(x)`
`q = 4Q or (Q)/(q) = (1)/(4)`