Advanced General Physics 323/324

Modern Physics Unit QM2 The Wave Nature of Matter

Overview: This unit introduces the idea that particles such as electrons and neutrons have wavelike properties and the probability interpretation of the wavefunction which reconciles these two seemingly contradictory properties.

Prerequisite: QM1

Read:

R. Eisberg and R. Resnick Quantum Mechanics of Atoms, Solids, Nuclei and Particles (2nd Ed.) , Chapt. 3 - de Broglie's Postulate--Wavelike Properties of Particles

Videotape: There is a videtape of a lecture by Prof. Mohan Kalelkar providing an explanation of the key concepts and problem-solving techniques for this unit. If you wish to view the tape during class ask your instructor to set you up in the nearby video room. This tape can also be viewed in the Math and Science Learning Center (MSLC) by asking at the reception desk for Physics 323 Tape QM2 on the Wave Nature of Matter.

The video may also be viewed online here

COMMENT:

You have studied the principal evidence that light has both a wave-like (Unit W1), and a particle-like nature (Unit QM1). Which aspect of light is evident in a particular experiment depends upon the experimental conditions. This strange property of light is called wave-particle duality.

Louis de Broglie suggested that matter also has a dual nature: in addition to its well-known particle nature it should also have wave-like properties which we can observe if we are ingenious, and which lead to the quantization of atomic energy levels.

This unit is devoted to learning how the wave-like properties of matter are manifested. On the experimental side you will learn about the famous Davisson-Germer experiment. On the theoretical side you will see that de Broglie's idea is compatible with classical kinematics (e.g. that a wave packet of momentum p_0 and mass m moves with a velocity p_0/m ), and that it leads to the well-known Heisenberg Uncertainty Principle.

After completing this unit you should understand:

  1. The de Broglie relations.
  2. Why the wave nature of matter is not evident in everday life.
  3. The Bragg Law.
  4. The uncertainty principle and some elementary applications.
  5. The probability interpretation of the wave function.

Problems:

Chapt. 3: Questions 1,2,4,10,12,13,15,17,18 and Problems 1,3,20.


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