Question

A charge having charge $e$ starting from rest from one conductor reaches the second conductor with a velocity $10cm{s}^{-1}$. If the $P.D.$ between them is $280V$ the mass of charge is :

• A. $8.96\times {10}^{-16}kg.$
• B. $8.96\times {10}^{-18}gm.$
• C. $8.96\times {10}^{-19}gm.$
• D. $8.96\times {10}^{-20}kg.$

Answer 1

The correct option is A $8.96\times {10}^{-16}kg.$

$P.D=280$V

$\Rightarrow$ K.E achieved after exhausting its P.E will be $e\times P.D=1.6\times {10}^{-19}\times 280$ Joule

but velocity $v=10$ m/s so K.E$=\frac{1}{2}m{v}^2$

both should be same

So, $1.6\times 280\times {10}^{-14}=\frac{1}{2}\times m\times 0.01$

$\Rightarrow m=\frac{3.2\times 2.8\times {10}^{-18}}{0.01}=8.96\times {10}^{-16}$kg