A toroid of n turns, mean radius R and cross-sectional radius a carries current I. It is placed on a horizontal table taken as x-y plane. Its magnetic moment m ______.

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A toroid of n turns, mean radius R and cross-sectional radius a carries current I. It is placed on a horizontal table taken as x-y plane. Its magnetic moment m is zero, otherwise there would be a field falling as 1/r^3 at large distances outside the toroid. Explanation: A toroid can be considered a ring-shaped closed solenoid. Hence it is like an endless cylindrical solenoid. The magnetic field is only confined inside the body of a toroid in the form of concentric magnetic lines of force. For any point inside the empty space surrounded by toroid and outside the toroid, the magnetic field B is zero because the net current enclosed in these spaces is zero. Thus, the magnetic moment of toroid is zero. [Solution diagram: 326902_solution_1.png] [Solution diagram: 326902_solution_2.png]

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