Question

An electric dipole with dipole moment $4 \times 10^{-9} C\,m$ is aligned at $30^{\circ}$ with the direction of a uniform electric field of magnitude $5 \times 10^{4} N\, C ^{-1}$. The magnitude of the torque acting on the dipole is

• A. $10^{-3} N m$
• B. $10^{-4} N m$
• C. $1.7 \times 10^{-3} N m$
• D. $1.7 \times 10^{-4} N m$

Answer 1

Answer: (B)

$\tau=p E \sin \theta=\left(4 \times 10^{-9} Cm \right)\left(5 \times 10^{4} N C ^{-1}\right) \sin 30^{\circ}$
$=10^{-4} N m$