When the radius of a circular current carrying coil is doubled and current in it is halved, the magnetic dipole moment of coil originally 4 units become.

Options

A. 18 unit
B. 16 unit
C. 8 unit
D. 4 unit

Answer

C

Explanation

Magnetic dipole moment, `M=iA`
Given current is halved, so `i_(1)=2i_(2)`, radius is doubled,
So, `r_(2)=2r_(1), M_(1)=4 units`
`(M_(1))/(M_(2))=(i_(1))/(i_(2))xx(pir_(1)^(2))/(pir_(2)^(2))`
`(4)/(M_(2))=2xx(1)/(4)`
`M_(2)=8 units`