Question

A positively charged particle of $2.0C$ moves upward into an area where both a magnetic field of the magnitude $4.0\times {10}^{-4}T$ and an electric field of the magnitude $0.1N/C$ are acting. Find out the velocity at which particle must move if it is not deflected when it enters this area?

• A. $4.0\times {10}^{-3}m/s$
• B. $125m/s$
• C. $250m/s$
• D. $500m/s$
• E. The particle will be deflected to the left regardless of its velocity

Answer 1

The correct option is C $250m/s$

Given : $E=0.1N/C$ $B=4.0\times {10}^{-4}T$

The electric force on the particle is canceled by the magnetic force so that the particle moves in the region with velocity $v$ without any deviation in its trajectory i.e $F_e=F_m$

$\therefore$ $qE=qvB$ $⟹v=\frac{E}{B}$

$v=\frac{0.1}{4\times {10}^{-4}}=250$ $m/s$