Download Introductory Experiments in the Physics Advanced Laboratory

Introductory Experiments in the Physics Advanced Laboratory
Physics 381
There are six introductory experiments in the physics advanced lab. These are:
The Speed of Light This involves reflecting a beam of light off a rotating mirror to a distant
mirror, which reflects the light back to the rotating mirror. Because this mirror has rotated, it
reflects the returning light slightly from its original path. Knowing the angle of this deflection,
the distance between the two mirrors, and the rotation frequency of rotating mirror allows one to
calculate the speed of light.
The Ratio of Specific Heat at Constant Pressure to the Specific Heat at Constant Volume
for a Gas Surprisingly, this measurement is made by timing the period of a ball “bouncing” on
a volume of enclosed air. By measuring the ratio of the specific heats, information about the
configuration of the atoms in the gas molecules is obtained.
The Ratio of Charge to Mass of an Electron A beam of electrons is produces with a known
velocity, and projected through a known magnetic field. The Lorentz force of the electrons, force
them to move in a circle. By measuring the diameter of the circle, the speed of the electrons, and
the strength of the magnetic field one can determine the ratio of charge to mass of the electron.
Rowland Spectrometer and Atomic Spectra Light from a gas discharge tube, is projected on a
concave diffraction grating mount in a Rowland spectrometer. The viewing position of known
spectral lines emitted by known elements are then used to calibrate the spectrometer. Unknown
elements are then identified using this calibration.
Fast Fourier Transforms and the Speed of Sound in Air Sound is digitized by a computer
and analyzed into the frequencies that make up the sound using fast Fourier transforms. Using an
“organ pipe” arrangement sound with known wavelengths are produce. Combining the
wavelengths and the frequency of a sound yields the speed of sound in air
Index of Refraction of Gases Light travels slower in air than in a vacuum, and this causes the
wavelengths to be shortened. If one measures the wavelength of a the light emitted by a laser in
a gas while varying the gas pressure, one can determine the index of refraction of the gas. The
measurement of the wavelength can be done using a Michelson interferometer that contains a gas
cell of known length. As the gas pressure within the cell is varied, the optical path of that leg of
the interferometer changes. Counting the interference fringes “moving” past a point lets one
measure enough about the wavelength to determine the index of refraction.
READING:
Data Reduction and Error Analysis for the Physical Sciences, 2nd Edition by P.R.Bevington and
D.K.Robinson,
Introduction to error analysis and statistics,: p 1-15,
Good general comments about statistics: p.57,58,
Significant figures: p. 4,14-15 ( rules on pages 14-15),
Averages and uncertainty of an average,: p. 53-57, 71 ( equations on page 71),
Error propagation: p. 41-50 ( equations on page 50),
Linear least squares analysis: p. 96-114 (equations with errors pages113,114 and for the special
case where all uncertainties are equal is page 104 halfway down).
OR
Experiments in Modern Physics, by A.C.Melissinos,
Error Propagation: p.467-473,
Averages and uncertainty of an average,: p. 446-447, and
Least squares analysis: p 462-463.
THINGS TO REMEMBER TO DO IN YOUR LAB NOTEBOOK
Schematic drawing(s) of the experimental setup
Equipment list
Settings of equipment controls
Significant figures
Full size plot of your data, with errorbars
Include references
Derivation of the working equation
Error analysis
A one page summary of results ( with references to lab notebook pages) containing:
Working equation.
Error propagation equation.
Values and uncertainties of each directly-measured parameter which appear in the
working equation.
Ratio of uncertainty to value for directly measured parameters that appear in the error
propagation equation.
Comparison with previous measurements