A toroid has `2000` turns. The inner & outer radii of its core are `11cm` and `12cm` respectively. The magnetic field in the core for a current of `0*7A` is `2*5T`. What is relative permeability of core?

Answer

`1026*9`

Explanation

Mean radius `=r=(11+12)/(2)=11*5cm`
`=11*5xx10^-2m`
`:.` No of turns/length
`n=(N)/(2pir)=(2000)/(2pixx11*5xx10^-2)`
As `B=munI`, where `B=2*5T` and `I=0*7A`
`:. mu=(B)/(nI)=(2*5xx2pixx11*5xx10^-2)/(0*7xx2000)`
`=12*91xx10^-4TmA^-1`
`mu_r=(mu)/(mu_0)=(12*91xx10^-4)/(4pixx10^-7)=1026*9`