Two concentric circular coild X and Y or radii 16 cm and 10 cm, respectively, lie in the same vertical plane oriented along the north to south direction. Coil X has 20 turns and carris a current of 18A. The sense of the current in X is anticlockwise and in Y is clockwise, for an observer looking at the coils facing west. Give the magnitude and direction of the net magnetic field due to the coils at their centre.

Explanation

`B=(mu_(0)nI)/(2a)`[ n= no. of turns, I= currents, a= radius of the coil]
`:.` for coil, X,
`B_(X)=(4pi xx10^(-7)xx20xx6)/(2xx16xx10^(-2))`
`=4pi xx10^(-4)T`(towards east)
For coil, Y
`B_(Y)=(4pixx10^(-7)xx25xx18)/(2xx10xx10^(-2))`
`=9pixx10^(-4)T`(towards west)
Net field `B_(Y)-B_(X)=9 pi xx10^(-4)-4pixx10^(-4)`
`=1.6xx10^(-3)T` (towards west)