Question

A coil of one turn is made of a wire of certain length and then from the same length a coil of two turns is made. If the same current is passed in both the cases, then the ratio of the magnetic induction at their centres will be :

(A) 2 : 1 

(B) 1 : 4

(C) 4 : 1 

(D) 1 : 2

Answer 1

Correct Answer is: (B) 1 : 4

Magnetic induction at the centre of current carrying coil

Suppose the length of the wire be L.

Ist case : For coil of one turn, let radius be r₁.

Ist case :

2nd case : For coil of two turns, let radius be r₂.