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An electric dipole is formed by two equal and opposite charges q with separation d. The charges have the same mass m. It is kept in a uniform electric field E. If it is slightly rotated from its equilibrium orientation, then its angular frequency ω is

Asked in JEE Main 8th April 2nd Shift 2019 · Oscillation of a dipole

Answer: (1) √(2qE)/(md)

Step-by-step solution

For a small angular displacement θ from the aligned position, the restoring torque is τ=-pE sin θ≈-pEθ, with p=qd.

The dipole rotates about its centre of mass, which is the midpoint, so each charge is at d/2 and I=2m(d/2)²=(md²)/2.

Iθ=-pEθ gives ω²=(pE)/I=(qdE)/(md²/2)=(2qE)/(md).

ω=√(2qE)/(md).

Why the other options are wrong

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