Two opposite and equal charges `4 xx 10^(-8)` coulomb when placed `2 xx 10^(-2) cm` away, form a dipole. If dipole is placed in an external electric field `4 xx 10^(8)N//C`, the value of maximum torque and the work done in rotating it through `180^(@)` will be

Options

A. `64 xx 10^(-4) Nm` and `64 xx 10^(-4) J`
B. `32 xx 10^(-4) Nm` and `32 xx 10^(-4) J`
C. `64 xx 10^(-4) Nm` and `32 xx 10^(-4) J`
D. `32 xx 10^(-4) Nm` and `64 xx 10^(-4) J`

Answer

D

Explanation

Dipole moment `p = 4 xx 10^(-8) xx 2 xx 10^(-4) = 8 xx 10^(-12) m`
Maximum torque `= pE = 8 xx 10^(-12) x 4 xx 10^(8)`
`= 32 xx 10^(-4) Nm`
Work done in rotating through `180^(@) = 2pE`
`= 2 xx 32 xx 10^(-4) = 64 xx 10^(-4) J`