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 values are possible charges of those oil droplets? − 8.0 × 10 − 19 C − 3.2 × 10 − 19 C − 1.2 × 10 − 19 C − 5.6 × 10 − 19 C − 4.8 × 10 − 19 C − 9.4 × 10 − 19 C

Every possible charged particle must have a charge that is an exact multiple of that elemental charge. For example, if a particle has 5 electrons in excess, thus its charge is [tex]5\times -1.6\cdot 10^{-19}\ C=-8 \cdot 10^{-19}\ C[/tex]

Let's test the possible charges listed in the question:

[tex]-8.0 \times 10 ^{-19 }[/tex]. We have just found it's a possible charge of a particle

[tex]-3.2 \times 10 ^{-19 }[/tex]. Since 3.2 is an exact multiple of 1.6, this is also a possible charge of the oil droplets

[tex]-1.2 \times 10 ^{-19 }[/tex] this is not a possible charge for an oil droplet since it's smaller than the charge of the electron, the smallest unit of charge

[tex]-5.6 \times 10 ^{-19 },\ -9.4 \times 10 ^{-19 }[/tex] cannot be a possible charge for an oil droplet because they are not exact multiples of 1.6

Finally, the charge [tex]-4.8 \times 10 ^{-19 }\ C[/tex] is four times the charge of the electron, so it is a possible value for the charge of an oil droplet

Summarizing, the following are the possible values for the charge of an oil droplet:

[tex]-8.0 \times 10 ^{-19 }\ C,\ -3.2 \times 10 ^{-19 }\ C, -4.8 \times 10 ^{-19 }\ C[/tex]