Chapter 11: Absorbed Photons and the Photoelectric Effect

11.1 Introduction to the Photoelectric Effect

The photoelectric effect is a phenomenon where light shining on a material causes the emission of electrons. This effect played a crucial role in the development of quantum mechanics, as it provided evidence for the particle-like nature of light and led to the concept of photons as discrete packets of energy.

11.2 The Photoelectric Effect Experiment

In a typical photoelectric effect experiment, a light source illuminates a metal surface, causing the emission of electrons. These ejected electrons are then collected by a positively charged electrode, creating a current. The following observations are made in such an experiment:

1. There is a minimum frequency, called the threshold frequency below which no electrons are emitted, regardless of the light intensity.
2. The number of emitted electrons is proportional to the intensity of the incident light.
3. The maximum kinetic energy of the emitted electrons is independent of the light intensity. It depends only on the frequency of the incident light.

11.3 The Photon Model of Light

The photoelectric effect could not be explained by classical wave theory. Albert Einstein proposed a photon model of light, where light consists of discrete packets of energy called photons. The energy of a photon is directly proportional to its frequency:

where is the energy of the photon, is the Planck constant ( Joule seconds), and is the frequency of the light.

11.4 Work Function and the Photoelectric Effect Equation

The work function is the minimum energy required to remove an electron from a material’s surface. Thus, when a photon with energy greater than the work function strikes the surface, an electron is emitted with a maximum kinetic energy given by:

This equation is known as the photoelectric effect equation, and it expresses the relationship between the incident photon energy, the work function, and the maximum kinetic energy of the emitted electrons.

11.5 Applications of the Photoelectric Effect

The photoelectric effect has various applications in modern technology, including photovoltaic cells for solar energy conversion, photomultiplier tubes for amplifying weak light signals, and photoelectron spectroscopy for analyzing the electronic structure of materials.

Chapter Summary

In summary, the photoelectric effect is the emission of electrons from a material when it is exposed to light. This phenomenon led to the development of the photon model of light and the quantization of energy. The photoelectric effect equation relates the incident light frequency, the work function of the material, and the maximum kinetic energy of the emitted electrons. The photoelectric effect has numerous practical applications in modern technology and continues to be an essential concept in the study of quantum mechanics.

Continue to Chapter 12: Emitted Photons and X-Ray Production

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