A closely wouhnd flat circular coil of 25 turns of wire has diameter of 10 cm which carries current fo `4 A` , the flux density at the centre of a coil will be

Options

A. `1.256 xx 10^(-3) T`
B. `1.679 xx 10^(-5) T`
C. `1.512 xx 10^(-5) T`
D. `1.28 xx 10^(-4) T`

Answer

A

Explanation

The magnetic field at the centre of the coil is
`B = (mu_(0))/(4pi) (2piNi)/(a)`
where `N` is number of turns, `t` is current and `a` is radius of coil.
Given, `N = 25, D = 10 cm = 10 xx 10^(-2)m`
`a = (D)/(2) = (10 xx 10^(-2))/(2) = 0.05m`
`t = 4A`
`:. B = 10^(-7) xx (2xx3.14xx25xx4)/(0.05)`
or `B = 1.256 xx 10^(-3)T`