Unexpected Result [ENDORSED]

[Rachel Min]

Just wanted to confirm that the unexpected result of the photoelectric experiment was that the intensity of radiation had no effect on the amount of electrons booted off the metal as long as the wavelength wasn't right? I'm still slightly confused.

[Sara Varadharajulu]

Hi Rachel,

You are right---if light mirrored a wave, changing the intensity, or the amplitude of the wave, should have increased the energy of the wave and booted off an electron. However, in this instance, light is behaving light a particle. This means that changing the intensity, or the number of particles, has no effect on the amount of electrons booted off. Each particle must have sufficient energy to remove an electron, so simply increasing the intensity will not help; the initial frequency must be high enough/wavelength must be short enough. Once the energy of the light has reached the threshold level, increasing the intensity will boot off more electrons.

[Leah Savage 2F]

Remember that intensity means different things for waves and for particles. Intensity of a wave corresponds to the amplitude of a wave, whereas increasing intensity for particles is just increasing the numbers of particles. If you have 400 photons and none of them are ejecting electrons and you up the intensity and 400 more of the same energy, then you're just going to have a lot of photons none of which have enough energy to eject an electron. What you have to do is up the frequency of the radiation, which increases the energy of the individual photons. This was surprising because experimenters initially thought that increasing the intensity would increase the amplitude of the wave and this would cause waves to eject electrons, but in this case we're not seeing light as waves but as photons, and intensity means something different for photons.

[Guangyu Li 2J]

For the lights with long wavelength, they can hardly remove electrons from the metal surface even by increasing the intensity. This unexpected phenomenon hints that energies of the emitted electrons to be independent of the intensity of the incident radiation. Instead, the energies required to remove electrons depends on the energy of each photon( E=hv)

E(photons)-E(required)=E(excess)=Ek=1/2mv^2

[Rachel Min]

Thank you for all the explanations! They really helped.