Repeat measurement 10 times for different dm PHYS 1494 Experiment 6

Repeat measurement 10 times for different dm phys

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Repeat measurement 10 times for different d m ! PHYS 1494: Experiment 6 - Interferometer
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FP Interferometer: He-Ne Wavelength Plot d m vs. m (number of fringes): For each measurement, extract wavelength λ using above equation. Report average: Compare to accepted value of 632.8 nm PHYS 1494: Experiment 6 - Interferometer
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Michelson Interferometer: Setup PHYS 1494: Experiment 6 - Interferometer LASER Beam splitter Movable mirror Adjustable mirror Lens Viewing screen
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Michelson Interferometer: Procedure Remove lens in front of the laser. Follow procedures as in lab manual. Tips for setup: For best results, make sure the two beams are almost exactly on top of each other before placing lens in front of laser! Same tips as in FP apply to Michelson. Measurement of He-Ne laser wavelength: Same procedure: Measure fringes vs distance of movable mirror. Take 10 trials. Report Compare to accepted value and Fabry-Perot Interferometer. PHYS 1494: Experiment 6 - Interferometer
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Michelson Interferometer: Measure n air Change the optical path length of the beam by changing the pressure: A change in pressure causes a change in index of refraction. The schematic setup for the Michelson interferometer is going to be: PHYS 1494: Experiment 6 - Interferometer Change in pressure = change in index of refraction = different wavelength
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Vacuum Cell and Pump PHYS 1494: Experiment 6 - Interferometer Vacuum cell mounted on rotational pointer Vacuum hand pump Release toggle Pressure gauge
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Michelson Interferometer: Measure n air The vacuum cell will be at P atm initially. You will slowly pump out the air to change the pressure and count the number fringes that pass through a certain point Constrain the rotational pointer when pumping the air to prevent the vacuum cell from oscillating/rotating Pressure gauge reads cm Hg (not inches Hg) Unit conversion not important since we'll be only needing pressure differences (as long as you are consistent). PHYS 1494: Experiment 6 - Interferometer
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Calculate the Index of Refrection We already saw that the number of fringes passing a point when the index of refraction is changed is given by: Problem: neither n i nor n f are known. Solution: divide everything by the change in pressure: However: Δn/ΔP = α = constant Therefore: PHYS 1494: Experiment 6 - Interferometer Linear relation between number of fringes passing through a point ( m ) and change in pressure
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Michelson Interferometer: Compute n air Make at least 7 measurements of m and ΔP Convert m to Δn through: Note: Use λ 0 = 632.8 nm Plot ΔP vs. Δn: Determine slope α Now use P atm =76 cm Hg, P vac = 0 , n vac = 1 to compute n air : PHYS 1494: Experiment 6 - Interferometer
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Measuring the Index of Refraction of Glass PHYS 1494: Experiment 6 - Interferometer LASER Glass mounted on rotational pointer
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Measuring the Index of Refraction of Glass Similar principle as n air : change in OPT = change in pattern Due to the angle of the glass with respect to the axis of the laser, the beam will refract according to Snell's Law : PHYS 1494: Experiment 6 - Interferometer The incidence angle θ is related to
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  • Spring '08
  • CARLO
  • Diffraction, Light, Wavelength, Michelson interferometer

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