The Atomic Theory of Matter and the Discovery of Atomic Structure (Sections)Millikan deter...

The Atomic Theory of Matter and the Discovery of Atomic Structure (Sections)

Millikan determined the charge on the electron by studying the static charges on oil drops falling in an electric field (Figure). A student carried out this experiment using several oil drops for her measurements and calculated the charges on the drops. She obtained the following data:

Figure

Would the masses of the oil drops be changed significantly by any electrons that accumulate on them?

Figure Millikan’s oil-drop experiment to measure the charge of the electron. Small drops of oil are allowed to fall between electrically charged plates. The drops pick up extra electrons as a result of irradiation by X-rays and so became negatively charged. Millikan measured how varying the voltage between the plates affected the rate of fall. From these data he calculated the negative charge on the drops. Because the charge on any drop was always some integral multiple of 1.602 × 10-19 C, Millikan deduced this value to be the charge of a single electron.

(a) What is the significance of the fact that the droplets carried different charges?

(b) What conclusion can the student draw from these data regarding the charge of the electron?

(c) What value (and to how many significant figures) should she report for the electronic charge?