Question

An electric field of $1500V/m$ and a magnetic field of $0.04Wb/m^2$ act on a moving electron. The minimum uniform speed along a straight line the electron could have is.

• A. $1.6\times {10}^{15}m/s$
• B. $6\times {10}^{-16}m/s$
• C. $3.75\times {10}^{4}m/s$
• D. $3.75\times {10}^{2}m/s$

Answer 1

The correct option is C $3.75\times {10}^{4}m/s$

Let the electron move with speed $v$ perpendicular to both electric and magnetic field. The electric force and magnetic force must cancel each other for electron to move with constant speed in a straight line.

Hence $qE=qvB$

$⟹v=\frac{E}{B}=37500m/s$