PHYS 301          Study Guide for Section II               Chapters 4 and 5 

Chapter 4 and 5 deal with early quantum theory (1900--1925). The topics: Black Body Radiation; Photoelectric Effect; De Broglie Relation; Compton Effect, and the Bohr Model of the atom have been of paramount   importance in convincing scientists to  accept  and see the significance of quantum theory. You should understand the history and the concepts behind these topics and then be able to use the formulas associated with them to solve problems. Slides 1 -- 88 and 95 -104 on the above link provide a good review or early quantum theory.  Also check the Visual Quantum Mechanics link. Play with , e.g., the hydrogen emission spectra experiment. I have linked all the topics below. Use your notes and the textbook as the guide. Some of the links are elementary and some a little advanced. They should help supplement your notes and your book.

Ch.5  & 6 Early Quantum Theory:

The Nature of Light

300 years ago, scientists did now if light had a wave or particle nature. How does quantum theory resolve this problem. List  phenomena of light that can be explained by wave or particle nature of light. List  phenomena of light that require the wave nature for their explanation. What is a photon? What role does it play in the photoelectric effect and also in explaining the black body radiation curve?

Black Body Radiation

Read the supplementary notes and appropriate section in your book related to black body radiation

How did the experimental black body radiation curve agree or disagree with the Rayleigh-Jeans Law? What did Planck introduce to come up with his radiation law? How did the experimental black body radiation curve agree or disagree with Planck's Radiation Law? How are Wien's diplacemt law and Stefan-Boltzman law obtain from Planck's Radiation Law? ( Be able to describe the method, You do not have to reproduce the derivation). Be able to determine the temperature of a star using Wien's law. Be able to determine the total energy out put of a star unsung Stefan-Boltzman law.

Photoelectric Effect

How did Einstein explain the photoelectric effect? Be able to use Einstein's photoelectric equation to calculate, K.E of ejected electrons, work function, threshold frequency and.or wavelength etc. List everyday applications or some devices that utilize the photoelectric effect If a stopping potential (V) Vs frequency (f) is plotted, what will be the slope and Y intercept of the curve. What does the curve, its slope and intercept prove?

The Compton Effect

What is Compton effect? Write down an expression for the change in wavelength a photon suffers due to a collision with an electron that was at rest relative to the lab. What happens to the electron after the collision? Write down equations based on the laws of conservation of energy and momentum that govern this collision? Does the Compton effect prove that the photon is a particle or wave? Be able to explain. Be able to use the formula that summarizes the Compton effect in problems.

De Broglie Relation (Matter Waves)

What the main idea behind de Broglie's thesis? Write down de Broglie's relation and calculate the wavelength for  an electrons going at v =.5c  and 1000 kg car gong at 62.5 mph? Describe the Davisson-Germer electron diffraction experiment with the help of a sketch diagram. Be able to write down Bragg's Law. Using Bragg's law, be able to calculate the wave length of electrons that are incident on a crystal and compare the result  with the wavelength that is obtained using De Broglie relation. Refer to examples in you notes and the book. What does this comparison prove.

 

The Bohr Model for Single Electron Atoms . Electron Diffraction

Write down Balmer's original formula and use it to calculate the wavelengths of the four hydrogen spectral lines. Transform Balmer's formula into the Rydberg-Ritz formula. State the three postulates (assumptions) Bohr made to construct his model of the single electron atom. What is the value and significance of the Bohr radius? According to the Bohr model how are the emission and absorption spectra of an atom produced? Does the Bohr atom use the wave or particle nature of light? What is the reduced mass of an electron and a proton? How does using the reduced mass instead of the electron mass affect the Rydberg constant calculated using the Bohr model? What is the significance of the Frank-Hertz Experiment? How is the quntization of angular momentum (L = nh/2 pi) explained using the de Broglie relation? How does the quntization of L apply to energy levels of diatomic molecules? ( see page 141) How do ideas from the Bohr model apply to a harmonic oscillator?  (see page 143). What is the Correspondence principle? (see page 144) List some of the successes and limitations of the Bohr Model.