A charge q is placed at the centre of the line joining two equal charges Q. The system of the three charges will be in equilibrium if q is equal to:

Options

A. `-Q//2`
B. `-Q//4`
C. `+Q//4`
D. `+Q//2`

Answer

B

Explanation

For Equilibrium at B
`vecF_A+vecF_C=0 implies vecF_A=-vecF_C`
`implies (KQ^2)/((2x)^2)=-(KQq)/x^2 implies q =-Q//4`