Q 12-02-023NEETJEE MainMedium
An electron is accelerated from rest through a potential difference of $200$ V. Its final speed is ($e/m = 1.76 \times 10^{11}$ C/kg)
Answer: (D) $8.4 \times 10^6$ m/s
Concept. $eV = \dfrac12mv^2$.
Step 1. Speed. $\sqrt{2 \times 1.76 \times 10^{11} \times 200} \approx 8.4 \times 10^6$ m/s.
Answer. $8.4 \times 10^6$ m/s (Option D).
Solution by Sreeraj P, M.Sc Physics