An electron initially at rest, is accelerated through a potential difference of `200` volt, so that it acquires a velocity `8.4 xx 10^(6)m//s`. The value of `e//m` of elctron

Options

A. `2.76 xx10^(12)` C/kg
B. `1.76 xx10^(11)` C/kg
C. `0.76 xx10^(12)` C/kg
D. None of these

Answer

B

Explanation

Law of conservation of energy
`1/2 mv^2 = eV`
`implies e/m = v^2/(2V) = ((8.4 xx10^6)^2)/(2 xx200) = 1.76 xx10^(11) C//kg`