: When coherent light shines
through a diffraction grating, interference occurs. The wavelength of the light
can be calculated using this formula dsinθ = nλ
. Where lambda (λ) represents the wavelength of light, n
is the order of the interference
is the separation distance between the slits in the grating,
is the angle between the central maximum and the bright spot in question.
- n is the order of the
interference spot, where n=0 for the central maximum spot, ±1 for the first
order maximum spot, ±2 for the second order maximum spot, etc.
is the separation distance between the separate slits/grooves. You will assume that the information printed
on the slide is correct, in giving the number of grooves per millimeter. Use this to find d. Calculate the distance, d,
between slits in meters.
- θ is the angle
between the central maximum and the bright spot in question. Calculate the angle using trigonometry
- Darken the room. (Caution: use a low-power laser, avoid
contact with anyone's eyes.)
- Shine a laser through the diffraction grating at flat screen
of graph paper.
- Photograph the diffraction (interference) pattern seen on
- Enter your diagram of diffraction, illustrating how wavelength is calculated in this DropBox folder.
- Enter Data in this data table.
- On either side of the central maximum is a dimmer spot known
as first order maximum. This is a
location of constructive interference in which waves add. Measure the distance between the central
maximum and the first two maxima. (n=1, 2)
- Determine the distance between the diffraction grating and
the screen (Lx), and the
distance between the central maximum and a first order maximum (Ly).
- Calculate the angle (θ) between the central maximum and
the first order maximum as the arctangent (tan-1) of the ratio of Ly / Lx
- Calculate the wavelength (λ) of the laser light in
meters. dsinθ = nλ; λ =(dsinθ)/n
- Calculate the wavelength of the red, green and blue lasers.
Enter the values in the collaborative data table as requested.
- What are the average of the calculated wavelengths for the red, green and blue lasers?