A charge of `0.8C` is divided into two charges `Q_(1) and Q_(2)`. These are kept at a separation of 30 cm. The force on `Q_(1)` is maximum when

Options

A. `Q_(1)=Q_(2)=0.4C`
B. `Q_(1)=0.8C,Q_(2)` negligible
C. `Q_(1)` negligible ,`Q_(2)=0.8C`
D. `Q_(1)=0.2C,Q_(2)=0.6C`

Answer

a

Explanation

Let one charge is Q coulomb then another charge is `(0.8-Q)` coulomb.
`therefore` Force of attraction , `F=K(Q_(1)xxQ_(2))/(r^(2))`
`F=(KQ(0.8-Q))/(r^(2))`
For maximum force, `
(dF)/(dQ)=0`
`therefore(dF)/(dQ)=(k)/(r^(2))(0.8-2Q)=0rArrQ=0.4C`
`thereforeQ_(1)=0.4C,Q_(2)=0.4C`