Question

An electron is shot in a steady electric and magnetic field such that its velocity is $V$. Electric field $E$ and magnetic field $B$ are mutually perpendicular. The magnitude of $E$ is $1volt/cm$ and that of $B$ is $2tesla$. Now it happens that the Lorentz (Magnetic) force cancels with the electrostatic force on the electron , then the velocity of the electron is:

• A. $50$ $m{s}^{-1}$
• B. $2$ $cm{s}^{-1}$
• C. $0.5$ $cm{s}^{-1}$
• D. $200$ $m{s}^{-1}$

Answer 1

Answer: (A)

$50$ $m{s}^{-1}$

$\because$ magnetic force cancels with the electrostatic force,
so $qE=qvB$
or, $V=\frac{E}{B}$$=\frac{100}{2}$$=50m{s}^{-1}$