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

Answer

C

Explanation

`v = (E)/(B) = (3.2 xx 10^(5))/(2 xx 10^(-3)) = 1.6 xx 10^(8)` m/s
`r = (mv)/(qB) = (9.1 xx 10^(-31) xx 1.6 xx 10^(8))/(1.6 xx 10^(-19) xx 2 xx 10^(-3)) = 0.45`m