PHY 123 — Modern Physics
Course Description
Third course in a three-semester sequence for students in physics, the physical sciences, or engineering. Covers wave motion, physical optics, special relativity, and quantum mechanics, including the Schrödinger equation, the hydrogen atom, the uncertainty principle, radioactive transitions, statistical mechanics, and selected topics in solid state, nuclear, and particle physics.
Location & Time
Labs are held in B&L 165.
- Afternoon: 2:00 PM – 4:40 PM
- Evening: 4:50 PM – 7:30 PM
- Night: 7:40 PM – 10:20 PM
Statistics & Error Analysis
Prior to the first lab, go through the statistics & error analysis tutorial. Print out the accompanying document, and go through the examples.
Labs
Lab 1 — The Speed of Waves
Measure the speed of sound in air by finding the resonant lengths of a closed tube at a known frequency. In the second part, drive standing waves on strings of different linear densities under varying tension, and verify the dependence of wave speed on these parameters.
Lab 2 — Geometric Optics
Verify the thin lens equation by measuring image distances for converging and diverging lenses at various object positions, and characterize the difference between real and virtual images. Use combinations of lenses to construct simple optical systems such as a telescope and a compound microscope, measuring their magnifications.
Lab 3 — Wave Properties of the Electromagnetic Spectrum
Observe double-slit and single-slit interference and diffraction patterns using both a helium-neon laser and a microwave source. Measure the fringe spacings to calculate the wavelengths of each source and confirm that wave optics applies across a wide range of the electromagnetic spectrum.
Lab 4 — The Atomic Spectrum of Hydrogen
Use a diffraction grating spectrometer to resolve the visible emission lines of atomic hydrogen and measure their wavelengths. Calibrate the spectrometer with a sodium source and verify that the hydrogen wavelengths match the predictions of the Balmer formula, confirming the quantization of atomic energy levels.
Lab 5 — The Franck-Hertz Experiment
Accelerate electrons through argon vapor in a vacuum tube and measure the current at the anode as a function of accelerating voltage, reproducing the landmark 1914 experiment of Franck and Hertz. Identify the periodic current drops caused by inelastic collisions to determine the energy of the first excited state of argon and confirm the discrete nature of atomic energy levels.