Description of Phyx 335-0 Physics Labs


This page contains a brief description of each of the labs associated with the 335-0 lecture. A more detailed write-up is available prior to the week of each lab. Lab times are scheduled through Dr. Schmidt. Students are expected to work on their own with a minimum of instruction in groups of two or three. The lab room is Tech MG11.

Lab 1:  Electron Diffraction from a Crystal Lattice

One of the more unfathomable facts for students of physics is that the familiar electron, a fundamental particle, in fact has wave properties associated with it.

This experiment involves an evacuated glass tube in which an electron gun has been packaged with a powdered aluminum target. The electron gun produces a beam of electrons that is aimed at the powered aluminum target, creating rings of scattered electrons. The rings are the result of the interference of electron matter waves scattered off the various crystal lattices of the aluminum. The inside face of the tube is coated with a phosphor to make the electron beam and the scattered electrons visible. One can vary speed of the electrons by controlling the accelerating voltage of the electron gun with a variable voltage power source. By measuring the radii of the rings, the student can deduce the wavelength of the electron matter wave and compare it to the predicted wavelength according to the deBroglie formula for an electron of a given speed.

In addition, an alternate target of graphite is available. This macro-crystalline material gives spectacular Laue spot patterns, with the spots arranged in a hexagonal array that fills the screen. Measurements of the spacings of these dots yield intermolecular distances which can be checked against other independent measurements.

Lab 2:  Planck's Constant and the Photoelectric Effect

A photoelectric tube is placed in a circuit with a current meter and a variable voltage power source. The tube is exposed to several different frequencies of light and the stopping potential for the photocurrent is measured. A plot of the stopping potential as a function of wavelength of light yields Planck's constant.

Our unique contribution to this experiment is that we will employ a holographic grating with a mercury light source to obtain clean, monochromatic light of known wavelengths. Holographic gratings have high transmission characteristics and very high dispersion compared to standard replica gratings, and are more commonly available at low cost.

Lab 3:  Pulsed Nuclear Magnetic Resonance

Electronic signature signals of nuclear spin resonances in a strong magnetic field are observed on an oscilloscope in response to radiating several different samples with pulsed of high frequency signals.

Lab 4:  Alpha, Beta & Gamma Radiation Sources

A Geiger tube connected to a computer-based rate meter can be used to explore various aspects of radiation. The relative penetrability of sources of alpha, beta, and gamma radiation through various materials such as aluminum and cardboard can be measured with a simple experimental set-up.

Lab 5:  Energy Spectrum of a Beta Source

A beta-emitting source is placed so that its emissions pass through the gap between the poles of a pair of permanent magnets. A Geiger tube is used to scan the beam of beta particles as they are dispersed by the magnetic field. The radiation spectrum of the beta particles is observed and analyzed.

Lab 6:  Scintillation Detector Experiment

A sodium iodide scintillation detector is used to measure the energies of gamma-rays emitted by a sample of cobalt-60

Lab 7: Half-lives of Airborn Radiation - The Radon Decay Chain

A simple balloon, rubbed to charge it electrically, will attract dust from the room air. It will also conveniently concentrate radioactive particles in the air which result from naturally occurring decays of heavy elements in the concrete and other building materials around us. A Geiger tube connected to a computer-based rate meter can be used to gather data on the decay rate, which can be analyzed to yield the lifetimes of some of these radioactive elements.