Question

A beam of electrons is moving with constant velocity in a region having simultaneous perpendicular electric and magnetic fields of strength 20V/m and 0.5T respectively at right angles to the direction of motion of the electrons. Then the velocity of electrons must be

• A. 8 m/s
• B. 20 m/s
• C. 40 m/s
• D. (1/40) m/s

Answer 1

The correct option is C 40 m/s

Strength of magnetic field $B=0.5T$
Strength of electric field $E=20V/m$
So, velocity of electrons $v=\frac{E}{B}$
$⟹v=\frac{20}{0.5}=40m/s$