An electron moves perpendicular to uniform magnetic field B, on a circle of radius r. Now, if magnetic field is made half of its initial value, what would be new radius of circular path ?

Options

A. `r/2`
B. `r/4`
C. 2r
D. 4r

Answer

C

Explanation

For uniform circular motion,
`(mv^(2))/r=Bqv`
`thereforer=(mv)/(Bq)`
`thereforerprop1/B" "[becausem,v,q" are same"]`
`thereforer_(2)/r_(1)=B_(1)/B_(2)=B/(B/2)`
`thereforer_(2)/r=2`
`thereforer_(2)=2r`