Question

An electric dipole is placed at an angle of $30^{o}$with an electric field of intensity $2 \times 10^{5}NC^{- 1}$.It experiences a torque equal to 4 N m. The charge on the dipole if the dipole length is 2 cm is.

• A. 8 mC
• B. 4 mC
• C. 6 mC
• D. 2 mC

Answer 1

Answer: (D)

2 mC

Answer 2

: Here, $E = 2 \times 10^{5}NC^{- 1}$

$l = 2cm,\tau = 4Nm$

Torque, $\overrightarrow{\tau} = \overrightarrow{P} \times \overrightarrow{E} = pE\sin\theta$

$\therefore 4 = p \times 2 \times 10^{5} \times \sin 30^{o}$or $p = 4 \times 10^{- 5}Cm$

As $P = ql$

$\therefore$Charge, $q = \frac{p}{l} = \frac{4 \times 10^{- 5}Cm}{0.02m}$

$= 2 \times 10^{- 3}C = 2mC$