Magnetism and Matter - Result Question 4

7. A coil in the shape of an equilateral triangle of side l is suspended between the pole pieces of a permanent magnet such that B is in the plane of the coil. If due to a current in the triangle a torque τ acts on it, the side l of the triangle is

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(a) 23(τB.i)12

(b) 2(τ3B.i)12

(c) 23(τB.i)

(d) 13τB.i

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Answer:

Correct Answer: 7. (b)

Solution:

  1. (b) τ=MBsinθ

τ=iABsin90

A=τiB

Also, A=1/2(BC)(AD)

But 12(BC)(AD)=12(l)l2(l2)2

=34l234(l)2=τBi

l=2(τ3B.i)12



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