An electron having charge `1.6xx10^(-19)C` and mass `9xx10^(-31)` kg is moving with `4xx10^(6)ms^(-1)` speed in a magnetic field `2xx10^(-1)` tesla in circular orbit. The force acting on electron and the radius of the circular orbit will be

Options

A. `18.8 xx10^(-13) N, 1.1 xx10^(-4) m`
B. `12.8xx10^(-14)N , 1.1 xx10^(-3)m`
C. `12.8xx10^(-13)N,1.1 xx10^(-3)m`
D. `1.28 xx10^(-13)N 1.1 xx10^(-4)m`

Answer

D

Explanation

Force acting on elctron
`F=Bev=2xx10^(-1)xx1.6xx10^(-19)xxx4xx10^(+6)N`
`=12.8xx10^(-14)N=1.28 xx10^(-13)N`
Now the radius of the circular orbit
`r=(mv)/(Bq)=(9xx10^(-31)xx4xx10^(6))/(2xx10^(-1)xx1.6xx10^(-4)m`