A planar coil of area 7 m2 carrying an anti-clockwise current 2 A is placed in an extemal magnetic field B=(0.2i^+0.2j^−0.3k^), such that the normal to the plane is along the line(3i^−5j^+4k^). Select correct statements from the following . ( Consider Normal of the coil and Magnetic moment vectors to be in the same direction )
This question has multiple correct options
A
The potential energy of the coil in the given orientation is 6.4J
B
The angle between the normal (positive) to the coil and the external magnetic field is cos−1(0.57)
C
The potential energy of the coil in the given orientatlon is 3.2J
D
The magnitude of magnetic moment of the coil is about 14 Am2
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Updated on : 2022-09-05
Solution
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Correct options are C) and D)
Area A=7m2, Normal n^=501(3i^−5j^+4k^) ≃71(3i^−5j^+4k^) ∴ area A=(3i^−5j^+4k^)m2 Magnetic field B=(0.2i^+0.2j^−0.3k^)T Current I=2A ∴ magnetic moment M=IA=(6i^−10j^+8k^)Am2 ∣M∣≃14Am2(2×7=14) Potential energy U=−M.B =−[1.2−2−2.4]=3.2J Let θ be the angle between n^ and B(i.e.,)between M and B. Now,U=−MBcosθ. ∴cosθ=−MBU=−14×0.43.2(∵0.17≃0.4) =−74=−0.57 θ=π−cos−1(0.57)