Photoelectric Effect

Introduction

Our objective in conducting this experiment was to observe a current passing through a photo tube. The photo tube consists of vacuumed Plexiglas tube, a metal spherical ball, and a metal circular plate, all in a circuit with a galvanometer and power supply. An ultraviolet lamp is kept separate and is used on the spherical metal ball. The effect of current is referred to as the photoelectric effect. We expect to see it as a result of excited electrons transferring through the vacuum to the other side, thus producing a current.

Theory

The photoelectric effect, a phenomenon in which electrons are emitted from matter after the absorption of energy from radiation from ultraviolet light, x-rays, etc. We can reasonably expect to observe this effect as a result of not only Einstein's Nobel Prize, but also an understanding of the Law of Conservation of Energy. An ultraviolet lamp was shone onto the spherical ball, exciting the electrons and satisfying the metal's work function. The work function, or ionization energy, of the metal is the amount of energy required to cause an exertion of electrons from the matter. If we were to instead use a source of light with a longer wavelength- thus a smaller amount of energy- the work function would not be satisfied. But the UV lamp is known to have sufficient energy to not only cause a release in electrons, but to have enough energy left over to provide them with a certain amount of kinetic energy.

This kinetic energy (Energy of light - Work function) allows some electrons to travel through the photo tube onto the conductive metal plate. The continuous flow of these electrons in a circuit thus creates a current: the photoelectric effect.