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Diffraction Grating - Wavelength of Light

PHY 201 & 231

Lab PDF 1
Lab PDF 2

Students separate light sources into component wavelengths using diffraction gratings. A series of measurements are made using a mercury light source and given wavelength values to determine the grating spacing. This value will then be used to determine the unknown constituent wavelengths of a helium source.


Name Location Quantity
Rods, Clip JE-105A-D24 2 per table
Gratings (Do Not Touch Window) JE-105A-D28 1 per table
Meter Stick - 1.00m JE-105A-(105 Door), D98 1 per table
Optics Bench Rod JE-105A (Next to File Cabinet) 1 per table
Clamp, Optics Bench JE-105A-D30, D31 3 per table
Optics Bench End Supports JE-105A-D31 2 per table
Ruler, Transparent, Flexible JE-105A-D90 2 per table
Spectral Tube Power Supply JE-105A-S145 1 per table
Spectral Tubes, Helium JE-105A-S145 1 per table
Spectral Tubes, Mercury JE-105A-S145 1 per table
Flashlights, Battery JE-105A-S140 1 per table
Lab Jack JE-105A-S38 1 per table
Aperture, Single/double Slit JE-105A-D28 1 per table
Tape, Masking JE-105A-D63 1 per table
Protractor JE-105A-D90 2 per table
Light Sources JE-105A-D29 1 per table


Install Hg spectral discharge tube in high voltage fixture and then arrange for smallest possible distance between the tube and aperture slit. Place the slits on measurement mark closest to the wall. The end clamp on the wall side should be slid on before the slit holder (not as pictured). The holder for the diffraction grating should be 100 cm from the slit. Separate the boxes that support the power supplies enough for the bar to slide between them. This allows the power supplies to get as close as possible to the slit. Make sure the slit is high enough to be on the brightest part of the light sources that are attached later in the experiment, yet low enough to be in front of the skinny portion of the spectral tubes. Leave He spectral tube on lab bench in safe and secure location. The single slit apertures are used in this lab. Mount high-efficiency (750 lines/mm) diffraction gratings in clip rod taking care to prevent clip from contacting window. Rest the spectral tube power supplies on empty hooked mass holders (found on shelf X36) or on other stable supports flanking optics bench to allow bulb to be very close to slit. For example, the lens holder blocks on S140 and the small blocks on S20 together can support the power supplies. Once the meter stick is held by another clip rod and leveled by the lab jack, tape down the end of the meter stick to the lab jack.

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Item modified on 2016-07-25 16:54:23 by damicoa6.