Question

If an electron moves from rest from a point at which potential is $ 50\text{ }V $ to another point at which potential is $ 70\text{ }V, $ then its kinetic energy in the final state will be

• A. $ 3.2\times 10^{-20}J $
• B. $ 3.2\times 10^{-18}J $
• C. $ 3.2\times 10^{-19}J $
• D. zero

Answer 1

Answer: (B)

The kinetic energy required by the particle is
$KE = q \Delta v$
Given, $q=e=1.6 \times 10^{-19} C$
$\Delta V=V_{2}-V_{1}=70-50=20 V$
$\therefore K E=1.6 \times 10^{-19} \times 20$
$=3.2 \times 10^{-18} J$