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Chapter 23: Quantum Physics

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Credit: Lawrence Livermore National Laboratory
Source: http://commons.wikimedia.org/wiki/File:AVLIS_laser.jpg
License: CC BY-NC 3.0

A copper vapor pump laser used in an atomic experiment. [Figure1]

As science began to look at very small sizes down to the scale of an atom, our previous intuition about matter broke donw.  Quantum mechanics is the solution to what seemed like inconsistent behavior of atoms and light, that resolves dilemmas over what is a wave and what is a particle.  Lasers create a precise wavelength due to quantum mechanics, and are increasingly found throughout everyday life.  This chapter covers black body radiation and Planck's quantum hypothesis, photons and the photoelectric effect, and wave-particle duality. 

Chapter Outline

Chapter Summary

1. The Planck equation relates the energy E of a photon of light to its frequency f

E=hf

where the constant h=6.626 \times 10^{-34} \ J-s is known as Planck’s constant.

According to the photoelectric effect, the maximum kinetic energy KE_{max} of the electrons ejected from a material is

KE_{max}=hf-W_o

where f is the frequency of the light incident upon the material and W_o is the work function of the material : the minimum energy needed to overcome the electrical forces that hold an electron within the material

W_o=hf_o

The frequency f_o corresponds to the minimum (threshold) frequency of light necessary to eject a photoelectron.

2. The De Broglie equation for the wavelength of matter waves is

\lambda = \frac{h}{mv}

where m is the mass of a particle, v its velocity and \lambda its associated wavelength.

Image Attributions

  1. [1]^ Credit: Lawrence Livermore National Laboratory; Source: http://commons.wikimedia.org/wiki/File:AVLIS_laser.jpg; License: CC BY-NC 3.0

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Date Created:

Jun 10, 2014

Last Modified:

Sep 06, 2014
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