Electrostatics Question 251

Question: An electric dipole is situated in an electric field of uniform intensity E whose dipole moment is p and moment of inertia is I. If the dipole is displaced slightly from the equilibrium position, then the angular frequency of its oscillations is [MP PET 2003]

Options:

A) x=d2

B) x=d2

C) x=d22

D) x=d23

Show Answer

Answer:

Correct Answer: C

Solution:

Suppose third charge is similar to Q and it is q So net force on it

Fnet= 2Fcosθ Where F=14πε0.Qq(x2+d24) and cosθ=xx2+d24

Fnet=2×14πε0.Qq(x2+d24)×x(x2+d24)1/2

=2Qqx4πε0(x2+d24)3/2

For Fnet to be maximum dFnetdx=0

i.e. ddx[2Qqx4πε0(x2+d24)3/2]=0

or [(x2+d24)3/23x2(x2+d24)5/2]=0 i.e. x=±d22



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