Friday, 20 June 2014 13:14

## M3-06: MICHELSON INTERFEROMETER - GAS CELL

• ID Code: M3-06
• Purpose: Show that the speed of light in air is different from the speed of light in a vacuum.
• Description:

The gas cell is positioned in one arm of the interferometer between the beam splitter and the moveable mirror such that the surfaces of the cell are perpendicular to the laser beam. After obtaining a clear set of fringes, pump some of the air out of the cell. Measure the pressure before and after and the number of fringes passed while pumping. The refractive index of the gas varies directly with its density, and the index of refraction of a vacuum is one. Thus a graph of refractive index as a function of pressure must go through the point x=0, y=1. Determine the slope of the line by calculating the change in the refractive index: if n1 is the index at the initial pressure and n2 is the index at the final pressure, then n1-n2=mL/2d, where m is the number of fringes counted, L is the wavelength, and d is the length of the gas cell (only the gas region, not the end plates).

The final photograph above is a detail of the fringe pattern. In the video linked below, you can see the fringes shift as air is pumped from the gas cell. You can hear the clicks from the hand pump as it removes air from the cell.

• Availability: Available
• Loc codes: FS1
• #### M3-01 MICHELSON INTERFEROMETER - LASER LIGHT

Shows laser light fringes using a Michelson interferometer Read More
• #### M3-02: MICHELSON INTERFEROMETER - WHITE LIGHT

Show white light fringes using a Michelson interferometer. Read More
• #### M3-03: MICHELSON INTERFEROMETER - MERCURY LIGHT

Show mercury light fringes with a Michelson interferometer. Read More
• #### M3-04: MICHELSON INTERFEROMETER - SODIUM LIGHT

Show the interference of sodium yellow light with a Michelson interferometer. Read More