Two equal point charges `Q=+sqrt(2) mu C` are placed at each of the two opposite corners of a square and equal point charges q at each of the other two corners. What must be the value of q so that the resultant force on Q is zero?

Answer

`(-1)/2 muC`

Explanation

`(F_(Q))_("total")=|vec(F)_(Qq)+vec(F)_(Qq)+vec(F)_(qQ)|`
`O=2F_(q) cos 45^(@)+F_(Q)`
`O=2xx1/sqrt(2)xx(KQq)/a^(2)+(KQ^(2))/(2a^(2))`
`q=(-Q)/(2sqrt(2))=sqrt(2)/(2sqrt(2))=-1/2 mu C`