Q. 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 θ with the direction of the field. Assuming that the potential energy of the dipole to be zero when θ = 90°, the torque and the potential energy of the dipole will respectively be
A) pE cos θ, −pE sin θ
B) pE sin θ, −pE cos θ
C) pE sin θ, −2pE cos θ
D) pE sin θ, 2pE cos θ
Explanation
[Solution from source] Torque on a dipole is τ = pE sin θ, and with U taken as zero at θ = 90°, the potential energy is U = −pE cos θ. The forms with 2pE cos θ wrongly double the energy, and pE cos θ is not the torque. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.