We conduct an experiment by shining 500

nm light on potassium metal. This causes electrons to be emitted from the surface via the photoelectric effect. Now we change our
source light to 450 nm at the same intensity level. Which of the following is the result from
the 450 nm light source compared to the 500 nm source?

I said that more electrons would be emitted. Is that correct? Thanks.

If the intensity level is in Watts, there will be fewer photons per second hitting the potassium because each photon carries more energy.

You need to know how the quantum efficiency for photoemission varies with wavelength in order to answer this question.

If the quantum efficiency is constant with wavelength between 450 and 500 nm, the photoemission current will go down, but there will be more energetic electrons.

Out of these choices what would you say?

1. The same number of electrons would be emitted, but they would have a lower velocity
2. The same number of electrons would be emitted, but they would have a higher velocity
3. No electrons would be emitted from the surface.
4. More electrons would be emitted from the surface.
5. Fewer electrons would be emitted from the surface.

Nevermind I figured it out myself.

Yes, you are correct. When we change the source light from 500 nm wavelength to 450 nm wavelength at the same intensity level, more electrons would be emitted compared to the initial condition.

This is because the energy of each photon of light is directly proportional to its wavelength. Photons with shorter wavelengths (like 450 nm) have higher energy compared to photons with longer wavelengths (like 500 nm).

According to the photoelectric effect, electrons can only be emitted from a metal surface when they absorb enough energy from incident photons to overcome the metal's work function. The work function is the minimum amount of energy required by an electron to be released from the metal.

Since the 450 nm light has higher energy photons compared to the 500 nm light, these higher energy photons will be able to transfer more energy to the electrons upon collision. As a result, more electrons will gain the necessary energy to be emitted from the metal surface. Therefore, the number of emitted electrons will increase when we change the source light to 450 nm at the same intensity level.