Magnetic induction at a point `(r,0^(@))` due to a short magnetic dipole is `B_(1)`.The magnetic induction due to the same dipole at a point`(r,60^(@))` is`B_(2)`.The ratio of `B_(1):B_(2)` is

Options

A. `1:1`
B. `sqrt(7):2`
C. `sqrt(7):4`
D. `4:sqrt(7)`

Answer

D

Explanation

`(B_(1))/(B_(2))=((mu_(0))/(4pi)(M)/r^(3)sqrt(3cos^(2)theta_(1)+1))/(mu_(0)/(4pi)(M)/(r ^(3))sqrt(3cos^(2)theta_(2)+1))`
`sqrt(3cos^(2)theta+1)/sqrt(3cos^(2)60+1)=(4)/sqrt(7)`