An electron is fired directly towards the center of a large metal plate that has excess negative charge with surface charge density `=2.0xx10^(-6) C//m^(2)`. If the initial kinetic energy of electron is 100 eV and if it is to stop due to repulsion just as it reaches the plate, how far from the plate must it be fired ?

Options

A. 0.44 mm
B. 0.20 mm
C. 1 mm
D. 0.30 mm

Answer

a

Explanation

Electric field due to large metal plate is `sigma//epsilon_0`. Since the electron has energy of `100 e V`, so it can cross a potential difference of `100 V` only. So
`100 = (sigma)/epsilon_0 d` (solve to get d.).