Photoelectric Effect

Background

In 1887, Heinrich Hertz was the first to observe the photoelectric effect that, amongst other observations of the subatomic world, led to the quantum revolution. Hertz witnessed electrons that were ejected from a metal when light was shone on it. The interesting find that led to quantum physics, and a separation from classical physics, is that the ability to eject the electron is based on the wavelength of the light. Neither the length of time that the light is shone, nor the intensity, determines if the electron is ejected, or determines its kinetic energy once ejected.

Photoelectric effect

 

For example, a red light shone on a metal surface might not eject an electron. A green light, with a shorter wavelength, might eject the electron. Whereas a blue light, with even shorter wavelength, might eject the electron with greater kinetic energy (velocity) than the green light. The red light could be shone for hours, much brighter than the blue light, and the results would be the same.

In 1905, Albert Einstein recognized that time and intensity were irrelevant in the experiment because light is “quantized” into packets. If light was a wave, it was expected prior to Einstein’s paper that it would be a continuous wave. Einstein proved it differently.

 


 

Explanation

In wave theory, light is a wave. It does not have mass as mass is defined as stored energy in standing waves. It is not a particle, as particles are defined by a formation of wave centers that create standing waves. Rather, it is a transverse wave that is created by a vibrating particle. The vibration is finite, leading to a defined volume for the wave, otherwise known as a photon. The figure below illustrates an electron’s path and the vibrating motion that creates the wave.

Electron Path - Transverse WaveElectron Path – Creating a Transverse Wave

 

The equations for transverse energy and wavelength contain an initial and final position for a particle that experiences a change in amplitude, which causes motion. However, it does not move from point A to point B like a man walking from his car into his home. Instead, a better analogy is a spring with a marble attached to the end. Stretch the spring and release it and the marble will move back-and-forth as the spring finds its equilibrium. As the electron changes orbits, it overshoots its final position, returns back (and overshoots again), and continues to repeat the process until it reaches equilibrium. This is the electron’s path in the figure.

Light is indeed a wave. It has a transverse component and a longitudinal traveling wave in a cylindrical shape. Einstein was also correct and it is a packet, or photon. In fact, two photons are generated, traveling in opposite directions from the vibrating particle.