During his experiments that confirmed the existence of electromagnetic waves, Heinrich Hertz used a spark across a gap between two electrodes to provide the rapidly changing electric current that produced electromagnetic waves. He noticed, however, that production of the spark required a lower voltage in a well-lighted laboratory than when the room was dark. Describe how this curious event can be explained in terms of the quantum interpretation of the photoelectric effect.

Video Transcript

This is College Physics Answers with Shaun Dychko. So we are told that Heinrich Hertz did some experiments where he was creating electric sparks between two electrodes and he noticed that the sparks were easier to make when the laboratory was well lit compared to when the room was dark so it required less voltage when there was light present. And so these photons in the light have energy equal to Planck's constant times the frequency and that energy was getting deposited in the electrodes and so if these are, you know, two electrodes between which there's going to be some sparks, a photon coming in and hitting this metal will tend to dislodge an electron and the electron will have some velocity— this is the photoelectric effect basically— and this electron will be easier to move now that it's been sort of removed from its atom and now less voltage will be required to make that electron do the jump across this air gap to the other electrode.