Question

Which of the following charges can not be present
on an oil drop in Millikan's experiment :-
(1) 4.0 × 10-19 C (2) 6.0 × 10-19 C
(3) 10.0 x 10-190 (4) all of them
​

Answer 1

MILLIKAN'S OIL DROP EXPERIMENT:

• Millikan's Oil Drop Experiment was aimed to calculate the charge of a single electron.

• Millikan's apparatus was built using parallel metallic plates with intervening insulating material and an electrostatic field.

• Electrically charged oil droplets were allowed to fall under gravity and was balanced by the Electrostatic Force.

Derived Equation:

$\therefore \: Eq = mg$

$\boxed{ = > q = \dfrac{mg}{E} }$

So, the charge of an electron was found to be

$\boxed{\large{e = 1.6 × 10^{-19}}}$.

Hence final answer is :

ALL OF THE ABOVE

Answer 2

Which of the following charges can not be present on an oil drop in Millikan's experiment.

(1) 4.0 × 10^-19 C (2) 6.0 × 10^-19 C

(3) 10 × 10^-19 C (3) All of them.

solution : according to Millikan's oil drop experiment, charge on each electron is -1.6 × 10^-19 C. it is the smallest charge which can exist in free state.

Most important point : charge is quantised. in mathematical form, Q = ne , where n must be positive integer.

where Q is charge on a substance, n is the number of electrons ejected/ added to the substance and e is charge on each electron.

1. Q = 4 × 10^-19 C ,

so, n = Q/e = (4 × 10^-19 C)/(1.6 × 10^-19) = (4/1.6) ≠ integer

so, it can not be present on an oil drop experiment.

similarly, (2) and (3) can not be present on the oil drop experiment.

Therefore the correct option is (4) all of them.