Question Video: Identifying an Atomic Theory or Experiment from a Diagram Chemistry • 10th Grade

Which of the following experiments or theories related to the charge of an electron does the diagram represent? [A] Bohr’s model of the atom theory [B] Rutherford’s gold foil experiment [C] Millikan’s oil drop experiment [D] J.J. Thompson’s cathode ray tube experiment [E] Dalton’s atomic theory

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Video Transcript

Which of the following experiments or theories related to the charge of an electron does the diagram represent? (A) Bohr’s model of the atom theory. (B) Rutherford’s gold foil experiment. (C) Millikan’s oil drop experiment. (D) J.J. Thompson’s cathode ray tube experiment. Or (E) Dalton’s atomic theory.

Experiments involving the device shown sought to discover the charge of the electron. These experiments followed shortly after the discovery of the electron by J.J. Thompson’s experiments. His work with cathode ray tubes showed that electrons were negatively charged particles within the atom with a tiny mass.

The experiment in the diagram built off of this knowledge to discover the exact charge of this electron. Droplets of oil were passed through a pinhole falling between two charged plates. At this point, they were ionized in the air using radiation. And so the particles of oil became charged. The scientists adjusted the voltage across the two plates until the charged oil droplets stopped moving and attained a state of mechanical equilibrium.

At this point of mechanical equilibrium, the downward force of gravity, or in other words the droplets’ mass, times the gravitational acceleration and the applied electric force or the charge times the electric field were equal. From this, the scientists were able to find the charge of the oil droplets. They found that all the oil droplets had a charge that was a multiple of a base unit. They found that this fundamental unit of charge was the charge of an electron. This experimental design is attributed to Millikan and is now famously known as Millikan’s oil drop experiment.

Therefore, the experiment or theory related to the charge of an electron represented by the diagram is answer choice (C), Millikan’s oil drop experiment.

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