CHEMISTRY COMMUNITY

In the photoelectric experiment when they doubled the intensity of light, electrons were still not ejected. What is intensity? Is the intensity the frequency or the wavelength?

I don't think intensity is related to either the frequency or the wavelength. When you double the intensity of light, you increase the number of photons emitted per second by the light source.

When you increase intensity of light, you are increasing the number of photons emitted by the light, not to be confused with the energy per photon emitted by the light. To increase the energy per photon of the light and therefore eject more electrons from the metal, you'd increase the frequency (decrease the wavelength) of the light.

I like to think of light intensity a how strong a light shines - the number of photons a light emits. If it changed frequency, i'd see a different color light. But Einstein's experiment shows that's what you need to do to knock off more electrons because colors with higher frequencies (lower wavelengths) have more energy in the photons they emit. This is also why increasing frequency also increases the KEmax of the ejected e-. All 3 terms describe light differently.

When light acts as a particle (as in the photoelectric effect), increasing intensity means increasing the # of photons.