Electric Charges and Fields - Result Question 18
18. An electric dipole of moment ’ $p$ ’ is placed in an electric field of intensity ’ $E$ ‘. The dipole acquires a position such that the axis of the dipole makes an angle $\theta$ with the direction of the field. Assuming that the potential energy of the dipole to be zero when $=90^{\circ}$, the torque and the potential energy of the dipole will respectively be :
[2012]
(a) $p E \sin \theta,-p E \cos \theta$
(b) $p E \sin \theta,-2 p E \cos \theta$
(c) $p E \sin \theta, 2 p E \cos \theta$
(d) $p E \cos \theta,-p E \cos \theta$
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Answer:
Correct Answer: 18. (a)
Solution:
- (a) The torque on the dipole is given as $\tau=p E \sin \theta$
The potential energy of the dipole in the electric field is given as
$U=-p E \cos \theta$
