Two plane parallel conducting plates `1.5xx10^(-2)m` apart are help horizontally one aove the other in air. The upper plate is maintained at positive potential of 1.5 kV while the other plate is earthed. Calculate the number of electorns which must be attached to a small oil drop of mass `4.9xx10^(-15)"kg"` between the plates to maintain it at rest. If the potential of upper plate is suddenly changed to `-1.5` kV, what is the initial acceleration of the charged drop ? Also obtain the terminal velocity of the drop if its radius is `5xx10^(-6)m` and coefficient of viscosity of air is `1.8xx10^(-5)N-s//m^(2)`. Assuming that the density of air is negligible in comparison with that of oil.

Explanation

`[3,19.6" ms"^(-2)"downward",5.7xx10^(-5)"ms"^(-1).]`