In a famous experiment done at the end of the 19th century, two metal electrodes were placed in an evacuated glass tube. A high voltage was applied between them. By using an appropriate metal for the cathode (e.g., sodium or potassium), it was found that a current could be made to flow when the cathode was illuminated with blue light, but no current would flow when red light was used, no matter how bright the light. Einstein was able to explain this strange phenomenon, and as a result, this experiment was considered the first experimental demonstration of
A) the particle nature of electrons.
B) the equivalency of electron and photons.
C) the wave nature of light.
D) the particle nature of light.
E) the wave nature of electrons.

Question

Quizplus · Accepted Answer

This experiment is a description of the photoelectric effect, which was explained by Albert Einstein. He proposed that light is made up of particles called photons, and the energy of these photons is dependent on their frequency. This was a key piece of evidence for the particle nature of light.

In a Famous Experiment Done at the End of the 19th