Measure the Wavelength of Light
What is the wavelength of a red or green or even violet laser beam? With some simple equipment and a little math, you can figure it out yourself!
Grades: 9 to 14
Duration: 1/2 Hour – 1 Hour
NGSS Connections PS4.B: Electromagnetic Radiation
- Use mathematical representations to support a claim regarding relationships among the frequency, wavelength, and speed of waves traveling in various media. (HS-PS4-1)
To set up, you will need a screen or blank wall; a laser source (Laser Pointer or LASER Blox), a meter stick, and a diffraction grating.
Set the laser securely on the table. Place the diffraction grating directly in front of the laser aperture. Place the screen 1m from the laser aperture as shown in the photo.
In step 2 you will be collecting data using the equation λ = (X) (d)/ L and solving for λ to find the wavelength of the laser you are using.
This video is a great summary on how to do this lab.
Take Measurements and Record Data
Download and fill in the Student Data Sheet in this step. You will need to take measurements and calculate 3 times to find an average.
Turn on the laser and observe the diffraction pattern on the screen.
You will use the data to calculate λ = (X) (d)/ L and solve for λ to find the wavelength of the laser you are using.
Notice that the diffraction grating tells you how many lines (tiny barriers) per mm – you must calculate the slit width: (d) in your equation.
L is the distance (in cm) from the diffraction grating (which should be right in front of the laser aperture, very close to the device) to the screen
Now look at the diffraction pattern. The CENTRAL dot is 0 (zero) order, the dots immediately to the left and right of the center dot are 1 and -1 order, with 1 to the right and -1 to the left. The next dots out on either side of them are order 2 and -2. X is the distance from the center dot to the first order dot, either + or -.
Once you have collected your data, insert your values into the equation λ = (X) (d)/ L and solve for λ to find the wavelength of the laser you are using.
You will need to work on converting your units to get the right answer – hint: the wavelength of light is generally stated in nM (nano meters)
Note that the SLIT WIDTH must be calculated from the Lines/mm of the Diffraction Grating. Students may need guidance or a review in how to manage the units to come out with the right final answer. The wavelength of light is generally stated in nM (nano meters).
Finally, compare your computed average with the stated wavelength on the laser label.