Question

A circular coil of wire consisting of 100 turns each of radius 9 cm carries a current of 0.4 A. The magnitude of the magnetic field at the centre of coil is `[ mu_(0) = 1256 xx 10^(-7)` Sl unit]
A. `2.4 xx 10^(-11) T`
B. `2.79 xx 10^(-5)T`
C. `2.97 xx 10^(-4)T`
D. `2.79 xx 10^(-3)T`

Answer 1

Correct Answer - C
Given number of turns n= 100 radius of coil `r = 9 cm = 9 xx 10^(-2) m`
and current flow in the coil , `I = 0.4A`
The magnitude of the meagnetic filed at the centre of a coil of n turns is given by
`B = (mu_(0)nl)/(2r) " "........(i)`
Substituting given values in Eq.(i) we, get
`rArr " " B = (1256 xx 10^(-7) xx 100 xx 0.4)/(2 xx 10^(-1) xx 9 xx 10^(-2))`
` = 2.97 xx 10^(-4)T `