An electron (mass `=9.1xx10^(-31)kg`, charge `=1.6xx10^(-19)C`) experiences no deflection if subjected to an electric field of `3.2`x`10^(5)V/m``, and a magnetic fields of `2.0xx10^(-3)Wb/m^(2)`. Both the fields are normal to the path of electron and to each other. If the electric field is removed, then the electron will revolve in an orbit of radius

Options

A. `45m`
B. `4.5m`
C. `0.45m`
D. 0.045m`

Answer

C

Explanation

For no deflection in mutually perpendicular electric and magnetic field `v=(E)/(B)=(3.2xx10^(5))/(2xx10^(-3))=1.6xx10^(8)m//s`.
It electric field is removed then due to only magnetic field radius of the path described by electron
` r= (mv)/(qB)=(9.1xx10^(-31)xx1.6xx10^(8))/(1.6xx10^(-19)xx2xx10^(-3))=0.45m`