# Diffraction Grating Experiment: Wavelength of Laser Light

### Objective

Calculate the wavelength of light.

### Materials

• Diffraction grating with lines of known separation
• Laser pointer with a known wavelength
• Metre stick
• Ruler
• Binder clips
• Index card
• Tape
• Protractor

### Procedure

1. Tape an index card to the wall so the blank side is facing you.
2. Lay the metre stick on a table or the floor so the 0 meets the index card.
3. Mount the later pointer at the end of the metre stick, pointing towards the index card.
4. Mount the diffraction grating a few centimeters from the index card so the lines are vertical.
5. Turn off the lights in the room and turn on the laser pointer.
6. Use your protractor to measure the angle between the metre stick and the first order visible band.
7. Use the formula Where λIs the wavelength, in meters DIs the distance in meters between lines on the diffraction grating θIs the angle and NIs the order. Unless the room is extremely dark, you will only be able to see the first order, so n=1.
8. Compare your calculated wavelength to the wavelength provided by the manufacturer of the laser.
9. Repeat for different lengths along the metre stick.

### Why?

Diffraction gratings Diffract, Or split, light Periodically, meaning the light splits into several beams with a given angular separation. In this experiment, the first Period, n=1, will be the brightest spot on the index card (besides the straight path of the laser, of course) after the grating splits the rays from the laser pointer. Using the formula above, you can verify the wavelength of light using what the manufacturer of the laser pointer says it is. If the room is dark enough, you may even be able to measure the 2NdAnd 3RdPeriods and plug n = 2 and n = 3 into your equation, respectively. It should yield the same result.

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