A wire of length l is used to form a coil. The magnetic field at its centre for a give current in it is minimum if the coil has

Options

A. `4 turn`
B. `2 turn`
C. `1 turn`
D. data is not sufficient

Answer

C

Explanation

(c) `B=(mu_0ni)/(2r)`
`implies l=2pirn, r=1/(2pi n)`
So, `B=(mu_0pi I n^2)/l implies B` is minimum if n=1