AP EAMCET · PHYSICS · Magnetic Effects of Current

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 \(m\)

A is non-zero and points in the z-direction by symmetry
B points along the axis of the toroid \((m=m \phi)\)
C is zero, otherwise there would be a field falling as \(\frac{1}{r^3}\) at large distances outside the toroid
D is pointing radially outwards

Verified Solution

Answer & Solution

Correct Answer

(C) is zero, otherwise there would be a field falling as \(\frac{1}{r^3}\) at large distances outside the toroid

Step-by-step Solution

Detailed explanation

We know that a toroid is a form of solenoid which is bend in the form of a circular coil. The magnetic field due to the toroid remains inside the circular coil of the toroid and it remains in the form of the concentric circles. The magnetic field outside the toroid is zero and…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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