The magnetic induction due to a short magnet at a distance of 20 cm on the axial line of a short bar magnet is `1.5xx10^(-6)" Wb/m"^(2)`. What is the magnetic induction at a point on its axis at a distance of 5 cm from the centre of the magnet?

Options

A. `6.4xx10^(-5)" Wb/m"^(2)`
B. `3.2xx10^(-5)" Wb/m"^(2)`
C. `9.6xx10^(-5)" Wb/m"^(2)`
D. `1.6xx10^(-4)" Wb/m"^(2)`

Answer

C

Explanation

For a short bar magnet, `B_("axis")=mu_(0)/(4pi) (2M)/d^(3)`
`:. B_(2)/B_(1)=(2M)/d_(2)^(3) xxd_(1)^(3)/(2M)=d_(1)^(2)/d_(2)^(3)=(20/5)^(3)=64`
`:. B_(2)/(1.5xx10^(-6))=64`
`:. B_(2)=64xx1.5xx10^(-6) =96xx10^(-6)=9.6xx10^(5)" Wb/m"^(2)`