Question

Two concentric coplanner coils of turns n1 and n2 have radii ratio 2: 1 respectively. Equal current in both
coils flows in opposite direction. If net magnetic field is zero at their common centre then n1:n2 is:-
(1) 2:1
(2) 1:2
(3) 1:1
(4) 4:1​

Answer 1

Answer:

2:1

Explanation:

The mag field produced by them are in opposit dirrection since they carry currents in opposit dirrection.. Therefore if the magnitude of the respective fields are equal, they will cancel and the net mag field at the centre will be zero..

B at centre is directly proportional to no turns and Inversely proportional to r

at centre is directly proportional to no N1/r1=N2/r2

=N1/N2=r1/r2

=2:1

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