Q 12-04-108JEE MainJEE Main 2023 (30 Jan, Shift 1)Easy
The magnetic moments associated with two closely wound circular coils $A$ and $B$ of radius $r_A=10\ \text{cm}$ and $r_B=20\ \text{cm}$ respectively are equal if (where $N_A$, $I_A$ and $N_B$, $I_B$ are number of turns and current of $A$ and $B$ respectively)
Answer: (C) $N_AI_A=4N_BI_B$
$m=NI\pi r^2$. Equal moments: $N_AI_A(10)^2=N_BI_B(20)^2\Rightarrow N_AI_A=4N_BI_B$.
Solution by Sreeraj P, M.Sc Physics