1.

The force of repulsion between two like or point charges + 2C and + 6C is 12 N, when charge q is added to both, the force of attraction between them will be 4 N, so q =......C.

Answer»

`+4`
`-4`
`+1`
`-1`

Solution :`F_(1) prop q_(1)q_(2)` and `F_(2) = q_(1)^(.)q_(2)^(.)`
`therefore F_(1)/F_(2) = (q_(1)q_(2))/(q_(1)^(.)q_(2)^(.))`
`therefore -12/4 = ((2)(6))/((2+q)(6+q))`
(By TAKING repulsive force .-ve and attractive force .+ve.)
`therefore 12 + 8Q + q^(2) =-4`
`therefore q+4=0`
`therefore q=-4 C`


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