A beam of electrons is moving with constant velocity in a region having simultaneous perpendicular electric and magnetic fields of strength `20Vm^(-1)` and 0.5 T, respectively at right angles to the direction of motion of the electrons. Then, the velocity of electrons must be

Options

A. `8m//s`
B. `20m//s`
C. `40m//s`
D. `1/40 m//s`

Answer

C

Explanation

The electron moves with constant velocity without deflection . Hence, force due to magnetic field is equal and opposite to force due to force due to electric field .
`qvB =qE implies v - E/B = 20/0.5=40m//s`