Two circular coils A and B having n and 2n number of turns have diameters 2d and d. If they carry the same current.
A] Which coil produces the maximum magnetic field at the centre ?
B] Which coil produces the minimum magnetic field at the centre ?

Explanation

Magnetic field `B prop (n l)/(d)`. Hence, for coil A, B `prop (2 n)/(d)` and for coil B, `B prop (2n)/(d)` .
Thus, answer are :A] Coil a B and B ] Coil A .