Question

The magnetic moments associated with two closely wound circular coils $A$ and $B$ of radius $r _{ A }=10$ $cm$ and $r _B=20 cm$ respectively are equal if : (Where $N _A, I _A$ and $N _B, I _{ B }$ are number of turn and current of $A$ and $B$ respectively)

• A. $2 N _{ A } I _{ A }= N _{ B } I _{ B }$
• B. $N _{ A }=2 N _{ B }$
• C. $N _{ A } I _{ A }=4 N _{ B } I _{ B }$
• D. $4 N _{ A } I _{ A }= N _{ B } I _{ B }$

Answer 1

Answer: (C)

$N _{ A } I _{ A }=4 N _{ B } I _{ B }$

Answer 2

Sol. M= NIA
MA​=MB​
∴NA​IA​AA​=NB​IB​AB​
∴NA​IA​π(0.1)2=NB​IB​π(0.2)2
∴NA​IA​=4NB​IB​