Question

A particle of mass m and charge q is placed at rest in a uniform electric field E and then released, the kinetic energy attained by the particle after moving a distance y, will be

• A. $ {{q}^{2}}Ey $
• B. $ qEy $
• C. $ q{{E}^{2}}y $
• D. $ qE{{y}^{2}} $

Answer 1

Answer: (B)

Force on charged particle in a uniform electric field is $ F=ma=Eq $ or $ a=\frac{Eq}{m} $ ?(1) From the equation of motion, we have $ {{\upsilon }^{2}}={{u}^{2}}+2ay=0+2\times \frac{Eq}{m}\times y $ $ =\frac{2Eqy}{m} $ Now kinetic energy of the particle $ K=\frac{1}{2}m{{\upsilon }^{2}}=\frac{m}{2}\times \frac{2Eqy}{m}=Eq\,y $