Textbook 1B.3

[Do Yeun Park]

The question is:
From the following list of observations, select the one that best supports the idea that electromagnetic radiation has the properties of particles. Explain your reasoning.

(a) Black-body radiation.

(b) Electron diffraction.

(c) Atomic spectra.

(d) The photoelectric effect.

Why don't Black-body radiation, electron diffraction, and atomic spectra support the answer? Could someone also explain the photoelectric effect supports this idea?

[Rhea Desai 1A]

I think the photoelectric effect just supports the idea the best. Black body radiation doesn't exactly relate to electromagnetic radiation acting like particles because it's more about the idea of absorbing all frequencies. Electron diffraction focuses on the wave aspect of electrons not electromagnetic radiation, and the atomic spectra is more related to the energy changes that come with electrons changing energy levels. The photoelectric effect best supports the idea of electromagnetic radiation acting like a particle because it explains how the radiation is made up of a stream of photons and how a photon can eject an electron because each photon has a certain amount of energy.

[Bryan Cheng 1H]

a. Black body radiation is outside the scope of this course (Dr. Lavelle briefly mentioned it, then told us we didn't have to worry about it).

b. Electron diffraction supports wave properties of electrons, not particle properties of light. Electrons are classically thought of as particles, but their diffraction patterns as shown in the double slit experiment show that they also have wavelike properties.

c. Atomic spectra don't support particle properties of light because they deal with electrons absorbing certain quantities of energy from light and causing dark lines in absorption spectra (or light lines in emission spectra), which has nothing to do with particle properties of light.

d. The photoelectric effect supports particle properties of light because of the photoelectric experiments conducted in the early 20th century. If the frequency of light applied did not give it enough energy to eject electrons from the substrate, no amount of increasing the intensity of light would cause ejection of electrons. However, if the frequency was raised and electrons were ejected, they would continue to be ejected even at low intensity of light. This went against classical thought about light's wave properties and confirmed Max Planck's theories about the existence of photons.