Question

A charge of +2 nC is separated from a charge of -2 nC by 1.5 cm forming an electric dipole. What torque acts on the dipole moment vector makes an angle of ${30}^0$ in the clockwise sense with the field of magnitude 5000 N/C?

Answer 1

Magnitude of dipole moment $P=ql=2\times {10}^{-9}\times 1.5\times {10}^{-2}=3\times {10}^{-11}Cm$

Angle between $P$ and $E$, $\theta ={30}^o$

Torque $\tau =PE\sin \theta$

Or $\tau =3\times {10}^{-11}\times 5000\times 0.5=7.5\times {10}^{-8}Nm$