Three charges Q, `+q and +q` are placed at the vertices of a right-angled isosceles triangle as shown. The net electrostatic energy of the configuration is zero if Q is equal to …………..

Options

A. `-2q`
B. `(-qsqrt(2))/(1+sqrt(2))`
C. `+q`
D. `(-2q)/(2+sqrt(2))`

Answer

B

Explanation

Net electrostatic energy, `U=(kQq)/(a)+(kq^(2))/(a)+(kQq)/(asqrt(2))=0`
`(kq)/(a)(Q+q+(Q)/(sqrt(2)))=0, Q=(-sqrt(2)q)/(1+sqrt(2))`