Question

The dipole moment of a circular loop carrying a current I, is m and the magnetic field at the centre of the loop is B₁. When the dipole moment is doubled by keeping the current constant, the magnetic field at the centre of the loop is B₂. The ratio  B₁ / B₂ is :
(1) √3 

(2) √2 

(3) 1/√2 

(4)2

Answer 1

Ans. (2)

Dipole moment of circular loop is m

moment becomes double ⇒ R becomes √2R (keeping current constant)