Q.

The magnetic moments associated with two closely wound circular coils A and B of radius rA=10 cm and rB=20 cm respectively are equal if (where NA,IA and NB,IB are number of turns and current of A and B respectively).              [2023]

1 2NAIA=NBIB  
2 NA=2NB  
3 NAIA=4NBIB  
4 4NAIA=NBIB  

Ans.

(3)

M=NIA

MA=MB

  NAIAAA=NBIBAB

  NAIAπ(0.1)2=NBIBπ(0.2)2

  NAIA=4NBIB