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 $K=\frac{1}{2}m{\upsilon }^2=\frac{m}{2}\times \frac{2Eqy}{m}=Eqy$