Question

The classic millikan oil drop experiment was the first to obtain an accurate measurement of the charge on an electron. in it, oil drops were suspended against the gravitational force by a vertical electric field. consider an oil drop with a weight of 4 x 10-14n, if the drop has a single excess electron, find the magnitude (in n/c) of the electric field needed to balance its weight.

Answer 1

Given Work none W = 4 x 10^-14 N 
Charge of electron q = 1.6 x 10^-19 C 
Formula for electric field E = W / q 
E = 4 x 10^-14 / 1.6 x 10^-19 = 2.5 x 10^5 N/C 
The Magnitude of the electric field is 2.5 x 10^5 N/C