Intensity of Light

[Semi Yoon]

What does it mean when light has high intensity? How is high intensity light different?

[Manya Bali 4E]

In addition to what we discussed in class, there's a really nice summary in the textbook that cleared up this concept for me. Hopefully, it's helpful for you too! I've posted it below.

Electromagnetic radiation (light) has wave-particle duality.
"In the wave model, the intensity of the radiation is proportional to the square of the amplitude of the wave. In the particle model, the intensity is proportional to the number of photons present at each instant" (Chemical Principles, Atkins, 6th Edition).

[AustinGrove3B]

Intensity of the light is directly proportional to the number of photons. So an intense light source will have more photons. Keep in mind that the intensity of the light has nothing to do with how much energy is in each photon (E=hv).

In terms of the photoelectric effect, shining a high intensity, but low frequency light will have a lot of photons hitting the metal surface. However, the photons don't have enough energy to eject electrons.

A low intensity light that has high frequency will have less photons hitting the metal surface, but the photons have sufficient energy to eject electrons.