Two identical short magnets, each of magnetic moment M, are placed with the same centre and their magnetic moments make an angle 120° with each other. The magnitude of their resultant magnetic moment is:
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Question

Two identical short magnets, each of magnetic moment M, are placed with the same centre and their magnetic moments make an angle 120° with each other. The magnitude of their resultant magnetic moment is:

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G1 Physics · Accepted Answer

The resultant of two vectors of magnitude M making angle 120° is M R M_R M R ​ = √(M²+M²+2M²cos120°). Since cos120° = -1/2, M R M_R M R ​ = √(2M²-M²) = M. Hence the resultant magnetic moment is M.