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Question

What should be the orientation of an electric dipole in a uniform electric field, that corresponds to stable equilibrium ?


A
θ=90
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B
θ=180
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C
θ=30
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D
θ=0
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Solution

The correct option is D θ=0
When the electric dipole aligns itself along the direction of electric field i.e p||E, then torque on dipole becomes zero.


Since, we know

τ=pEsinθ

τ=0, when θ=0 or θ=180

The net force on electric dipole is always zero in an uniform electric field.

Thus, τnet=0 & Fnet=0 corresponds to equilibrium position for dipole's orientation when θ=0 and θ=180.

Now electrostatic potential energy of dipole,

U=p.E=pEcosθ

U=pEcos0=pE

U=pE (when θ=0)

Similarly, U=pEcos180=(pE)

U=+pE (when θ=180)

Therefore, for θ=0, the potential energy is minimum.

Umin=pE

θ=0 corresponds to stable equilibrium position of dipole.

Why this question?Tip: The equilibrium position corresponding to θ=180 is unstable equilibrium because Potential energy of dipole is maximum

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