AL Physics: Photoelectric Effect
When a metal is exposed to electromagnetic radiation, electrons are emitted. Why is the classical wave theory unable to explain the phenomenon?
Does this mean that the radiation is not a wave? It seems strange.
If it is a wave, then the classical wave theory should be able to explain the phenomenon. If it is not a wave, then why we always call EM wave a wave?
- 志仁Lv 61 decade agoBest Answer
In classical, the electrons will be emmitted after it get enought energy under the exposion of EM wave for a period of time, no matter the wavelenght/frequency of the wave. By experiments showed that only for some radiation with higher frequency can make electrons emmition. If the frequency is lower than the a value, that will be no electron emmited.
The explaination of the photoelectric effect is, there is a particle nature in the EM radiation, called as photon. There is energy and also momentum in the photon, it energy is proportional the the frequency of the EM radiation, E=hf. Only photon will enough energy can "kick" the electron of the outermost shell of the metal.
PLEASE RMIND THAT EM RADIATION IS WAVE, AND ALSO WITH PARTICLE NATURE. There is call wave-particle nature. That mean that the EM radiation consisting the particle nature with the wave nature at the same time. When you are doing experiment like double slit interence, you can see its wave nature, while doing experiment like photoelectric, you can see its particle nature.
You should know that electron is particle. If you accelerate the electron up to the speed near light, and let it passes thought double slits, what do you expect you will observe? Assume there is many electrons with speed near c passing thought the double slits, you will see intereference pattern form at the wall/screen behide the the slits, same as the interence experiment you have done before. The electron beam is particle and at the same time, a wave. There is NO CONTRACDICTION FOR A "MATTER" TO BE A WAVE AND PARTICLE AT THE SAME TIME. You and me are both particle and wave, but it is very very hard to see our nature in wave. The particle nature is very important, it is the begining of the quantum physics.