changing \u03b8 will change the distance A to B that the beam travels and hence the

# Changing θ will change the distance a to b that the

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changing θ ) will change the distance A to B that the beam travels and hence the pattern PHYS 1493/1494/2699: Exp. 6 – Interferometers
35 Measuring the index of refraction of glass Applying Snell's Law and doing a little geometry we get the following expression for n glass : Start marker at zero, then rotate to some angle θ and count the number of fringe shifts . Use equation above for n glass , Take 5 more measurements for various angles . Take average and report: PHYS 1493/1494/2699: Exp. 6 – Interferometers
36 Tips Here are some (maybe) useful tips : 1. You will notice that the first fringe from the center is usually really thick while from the third on their are really thin. The best fringe to point for your counting is usually the second one 2. Setup is an essential part of the experiment. Do that as carefully as possible 3. Both the interferometers are really precise and they particularly suffer from vibration of the environment. Try to minimize them, for example, by not touching the table when performing a measure 4. The largest source of error is mostly likely mis-counting the number of fringes so assign a reasonably large error 5. When taking different data, always start counting from zero . This will avoid propagating mis-counted fringes 6. When using the micrometer is better to start measuring with respect to the 500 μm mark (linear response). Don’t forget to restart every time from there! PHYS 1493/1494/2699: Exp. 6 – Interferometers
37 Summary Using the Michelson and Fabry-Perot interferometer and changing the optical path length of the beam, we can hopefully measure many parameters from our system. Wavelength of He-Ne laser Index of refraction of air and glass. This can be be the most difficult and tedious experiment all semester: Need to show up prepared to lab!!! That being said, it has a large potential for high quality data and a clear analysis. PHYS W1493/W1494/W2699: Exp. 6 – Interferometers

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