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A 2 A current is flowing through two different small circular copper coils having radii ratio 1:2. The ratio of their respective magnetic moments will be

Asked in NEET 2025 · Magnetic moment of loops and charges

Answer: (3) 1:4

Step-by-step solution

Given: the same current 2 A in both coils, radii in the ratio 1:2.

Idea: m=IA for a single turn, and the area of a circle goes as the square of the radius.

m=Iπ r².

With the current the same in both, m∝ r².

(m₁)/(m₂)=((r₁)/(r₂))²=(1/2)².

=1/4, that is 1:4.

The value of the current never enters, since it is the same for both.

Why the other options are wrong

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