Question

When a certain length of wire is turned into one circular Loop, the magnetic induction at the centre of coil due to some current flowing is B₀. If the same wire is turned into three Loops to make a circular coil, the magnetic induction at the centre of this coil for the 

(a) B₀ 

(b) 9 B₀ 

(c) 3 B₀ 

(d) 27 B₀

Answer 1

  The correct option (b) 9 B₀

Explanation:

B = n²B₀

where n is number of loops

 here   n = 3

∴  B = (3)²B₀ = 9B₀

OR

B₁ = 10^–7 × [(2πI)/r]

B₂ = 10^–7 × [(2πI × 3)/(r/3)]

∴  = 9 × 10^–7 × [(2πI)/r]

B₂ = 9B₁

i.e.   B = 9B₀