Question

9. In Millikan's oil drop experiment an oil

drop is held stationary by p.d) of 400 V,
if another drop of double the radius bu
carries same charge is to be held
stationary, the p.d) required is
a) 800 V
b) 1600 V
c) 3200 V
d) 400 V
The strona​

Answer 1

From the figure, F
e
​
and F
g
​
represents electric and gravitational forces respectively.
We can observe that,

V∝
q
m
​


and in turn m∝r
3

given V = 400V is initial voltage and let V
1
​

substituting these values in the respective equations we get

V
V
1
​

​
=
r
3
(q)
(2r)
3
q
​


solving the above eqaution will give us
V
1
​
=8×V=3200 V
So, the answer is option (C).