Term Paper on Photoelectric Effect | Quantum Physics | Physics

Here is a term paper on photoelectric effect.

The photoelectric effect tested the classical wave theory of light, which was predominant at that point in time. In coming up with the solution to this dilemma, Einstein would gain a reputation in the physics community, eventually earning the Noble Prize in 1921.

The Photoelectric Effect was first observed in 1839, it wasn’t documented until 1887 in a paper by Heinrich Hertz. Basically a light source is incident upon a metallic surface, the surface emits electrons called photoelectrons.

In order to observe this effect, scientists would create a vacuum chamber with photoconductive metal at one end, plus a collector at the other end. By shining a light on the metal, electrons are released that move through the vacuum to the collector. As a result, a current is created in the wires connecting the two ends. This current is measured with an ammeter.

When administering a negative voltage potential to the collector, more energy is expended for the electrons to complete their journey, thus initiating a current. When no electrons find their way to the collector, this is called the stopping potential V_s, which can be used when defining the maximum kinetic energy of the electrons themselves.

Note that not all electrons have this energy, but will have a range of energies based upon the experimental metal’s properties. The equation created to calculate the maximum kinetic energy of the particles bumped free of the metal surface at a maximum speed.

Classic Wave Theory explained as energy of electromagnetic radiation being carried within the wave itself. As the wave collided with the metallic surface, the electrons absorb the wave’s energy until it exceeds the binding energy, thus releasing that electron from its metal surface.

This classic explanation includes three fundamental predications:

1. The resulting maximum kinetic energy should have a proportional connection with the strength of the radiation involved.

2. This effect will occur with any light, regardless of wavelength or frequency.

3. A delay will be witnessed of seconds between the radiation’s contact with metal and its first release of photoelectrons.

Yet the experimental results directly contrasted with these three predications:

1. Maximum kinetic energy of the photoelectrons wasn’t effected by the intensity of the light source.

2. The photoelectron effect was not observed below a certain frequency.

3. The delay was not observed between the radiation’s metallic contact and the emission of the first photoelectrons.

Since these are the exact opposite of what was predicted by the wave theory and completely counter-intuitive to what the scientists believed would occur. Einstein would publish a paper in 1905 that built on Max Planck’s black body radiation theory to explain the photoelectric effect and the contradictions scientists were observing. What he proposed was that radiation energy is not distributed equally over the wave front, but is localized into smaller bundles called photons.

The photon’s energy was associated with its frequency, along with its proportionality constant and the speed of light. The proportional constant could also be defined using the wave’s length.

According to Einstein, a photoelectron was released from an interaction with a single photon, rather than interacting with the whole wave. The energy transfers instantaneously to a single electron, knocking that electron free if the energy is high enough to break away from the metal’s work function.

If the energy or frequency is too low, there won’t be any electrons released. With excess energy, beyond what is available in the photon, this excess energy will be converted into the photon’s kinetic energy. So what Einstein put forward is that maximum kinetic energy is completely independent of light intensity. He was so confident that he didn’t even add the intensity of light into his equation.

When researchers shine twice as much light, they get twice as many photons, but the maximum kinetic energy itself doesn’t change unless the energy of the light, instead of its intensity changes. So when does the maximum kinetic energy occur? It results when the least-tightly bound electrons break free.

As for the more tightly bound photons, when they are knocked free there is a result of kinetic energy equal to zero. The result was equations that indicate why the low-frequency light couldn’t free any electrons, thus producing no photoelectrons.

Since Einstein, other experimentation has been carried out by Robert Millikan, not only confirmed Einstein’s theory, but also won Millikan a Nobel Prize in 1923. This experiment and the resulting data helped to crush the classic wave theory, as it was shown that light behaved as both a wave and a particle, commonly known now as the wave particle duality.

But other scientists were studying light and proving the wave theory with their experiments. One such experiment was the Young Double Slit Experiment.