Question

A body of $2g$ carrying a charge of $0.1\times {10}^{-6}C$ starts from rest from the positive plate and moves to the negative plate of a parallel plate condenser connected to a voltage supply of $30kV$. The final velocity is:

• A. $\sqrt{3}m{s}^{-1}$
• B. $\frac{\sqrt{3}}{12}m{s}^{-1}$
• C. $\frac{1}{\sqrt{2}}m{s}^{-1}$
• D. zero

Answer 1

The correct option is A $\sqrt{3}m{s}^{-1}$

Work done on particle: $W=\Delta V\times q$$=30\times {10}^3\times 0.1\times {10}^{-6}$$=3\times {10}^{-3}J$
All the Work done on the particle converts into it kinetic energy.
$\Rightarrow \frac{1}{2}m{v}^2=3\times {10}^{-3}$
or, $v^2=\frac{2\times 3\times {10}^{-3}}{2\times {10}^{-3}}$

or, $v=\sqrt{3}m{s}^{-1}$