The radius of the coil of a tangent galvanometer is `16cm`. How many turns of the wire should be used if a current of `40mA` is to produce a deflection of `45^@`. Given, horizotnal component of earth's field is `0*36xx10^-4`T.

Options

A. 458
B. 229
C. 200
D. 115

Explanation

Here, `r=16cm=0.16m,n?`
`I=40mA=40xx10^(-3)A`,
`theta=45^(@)H=0.36xx10^(-4)T`
As `(mu_(0)nI)/(2r)=Htantheta`
`therefore n=(2rHtantheta)/(mu_(0)I)`
`=(2xx0.16xx0.36xx10^(-4)tan45^(@))/(4pixx10^(-7)xx(40xx10^(-3)))`,
`n=229`