Two insulting plates are both uniformly charged in such a way that the potential difference between them is `V_2-V_1=20V`. (i.e., plate 2 is at a higher potential). The plates are separated by `d=0.1m` and can be treated as infinity large. An electron is released from rest on the inner surface of plate 1. What is its speed when it hits plate 2? (`e=1.6xx10^-19C`, `m_e=9.11xx10^-31kg`)

Options

A. `32xx10^(-19) m//s`
B. `2.65xx10^(6) m//s`
C. `7.02xx10^(12) m//s`
D. `1.87xx10^(6) m//s`

Answer

B

Explanation

Gain in kinetic energy = work done by `p.d.`
`(1)/(2) mv^(2) = e(V_(2) - V_(1))`
`v = sqrt((2e(V_(2) - V_(1)))/(m)) = sqrt((2xx1.6xx10^(-19)xx200)/(9.1xx10^(-31)))`
`v = 2.65xx10^(6) m//s`