Two electric dipoles each of dipole moment p=6.2×10−30C−m are placed with their axis along the same line and their centres at a distance d =10−8cm. The force of attraction between dipoles is:
A
2.1×10−16N
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B
2.1×10−12N
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C
2.1×10−10N
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D
2.1×10−8N
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Solution
The correct option is C2.1×10−8N Electric field due to a dipole on its axis is given by 2→p/(4πϵ0r3)
Therefore using necessary approximation and F=qE we get,
F=2qp/(4πϵ0)(1/(d−l)3−1/(d+l)3)=2qp/(4πϵ0)6d2l/d6=6p2/4πϵ0d4 putting in the values,