In the uniform electric field of `E = 1xx10^(4) "NC"^(-1)` , an electron is accelerated from rest . The velocity of the electron when it has travelled a distance of `2xx10^(-2)` m is nearly `(e/m " of electron " approx 1.8 xx10^(-11) C " kg"^(-1))`

Options

A. `8.5 xx10^(6)"ms"^(-1)`
B. `1.6 xx10^(6)"ms"^(-1)`
C. `0.85 xx10^(6)"ms"^(-1)`
D. `0.425 xx10^(6)"ms"^(-1)`

Answer

A

Explanation

By work - energy theorem ,
Work energy done by electric field = Change in KE of electron
or `qE x = 1/2 mv^(2)`
or ` v = sqrt((2qEx)/m)`
`= sqrt(2xx1.8 xx10^(11) xx1xx10^(4) xx2xx10^(-2))`
` = 8.5 xx10^(6) "ms"^(-1)`