Question

The smallest unit of charge is –1.6× 10–19 C, which is the charge (in coulombs) of a single electron. Robert Millikan was able to measure the charge on small droplets of oil by suspending them between a pair of electrically charged plates. Which of the following are possible charges of those oil droplets?

(1)– 1.2× 10 –19 C

(2)– 3.2× 10 –19 C

(3)– 4.8× 10 –19 C

(4)– 5.6× 10 –19 C

(5)– 9.4× 10 –19 C

Answer 1

As the charge on single electron is – 1.6× 10 –19 C

So the charge on muliken drop must be a multiple of this charge, it cannot be fraction of this

Let us check

(1)– 1.2× 10 –19 C : not a multiple of – 1.6× 10 –19 C : so this is not possible

(2)– 3.2× 10 –19 C : this is 2 X – 1.6× 10 –19 C so this is possible

(3)– 4.8× 10 –19 C: this is 3 X – 1.6× 10 –19 C so this is possible

(4)– 5.6× 10 –19 C : this is not multiple of – 1.6× 10 –19 C, so this is not possible

(5)– 9.4× 10 –19 C : this is not multiple of – 1.6× 10 –19 C, so this is not possible