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JEE Main 2019 (8 Apr, Shift 2) · Electric Dipole

Electric Dipole question from JEE Main 2019 (8 Apr, Shift 2)

Q67JEE Main 2019 · 8 APR · SHIFT 2Medium

Electric Dipole

An electric dipole is formed by two equal and opposite charges q with separation d. The charges have 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\omega is :-

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Answer: (d)

  1. Each mass mm at d2\frac{d}{2} from the centre: I=2m(d2)2=md22I = 2m\left(\frac{d}{2}\right)^2 = \frac{md^2}{2}.
  2. Restoring torque τ≈qdE θ\tau \approx qdE\,\theta.
  3. ω=qdEmd2/2=2qEmd\omega = \sqrt{\frac{qdE}{md^2/2}} = \sqrt{\frac{2qE}{md}}
  4. So the answer is (d).
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