*** DO NOT WRITE ON THESE INSTRUCTIONS!!! ***
Place all data and answer questions in your lab notebook.
MYIB / Honors Physics
Diffraction Lab Instructions
Objective: To calculate the spacing between the slits of a diffraction grating.
Materials: A laser, diffraction grating, paper, and meter sticks.
Caution: Lasers are used in this experiment. Under no circumstances should you look directly into the laser or at
its reflected light
Instructions:
1. On the laser, locate the wavelength of the light. Record this information in the data chart.
2. Keeping the laser horizontal, turn on the laser and shine the light onto a sheet of paper taped to the wall. If the
light does not shine onto the paper, adjust the height of the paper so that it does. It is important that the laser is
horizontal and is perpendicular to the wall. If it shines at an angle, it will affect the validity of that data collected.
3. You may wish to turn the laser off while performing this step to protect your eyes.
Choose a location along the beam of the laser to place the diffraction grating. Place the diffraction grating in this
location, and, with a meter stick, measure the distance between the grating and the paper. Record this value in the
data table.
4. Direct the laser beam through the diffraction grating so that a diffraction pattern is displayed on the paper.
With a writing utensil, mark the exact location of the central maximum as well as the first, second, third, and
fourth order maxima. Label this side of the paper as Trial 1.
5. Flip the paper over and re-tape it to the wall in the original location.
6. Choose a different location along the beam of the laser to place the diffraction grating. Place the diffraction
grating in this location, and, with a meter stick, measure the distance between the grating and the paper. Record
this value (in meters) in the data table.
7. Repeat step 4, however, label this side of the paper as Trial 2.
8. At this point, turn off the laser.
9. From trial 1 measure the distance between the central maximum and the first order maximum. Record this
value (in meters) in the data table.
10. From trial 1, measure the distance between the central maximum to the third order maximum. Record this
value (in meters) in the data table.
11. Repeat steps 9 and 10 for trial 2.
*** DO NOT WRITE ON THESE INSTRUCTIONS!!! ***
Place all data and answer questions in your lab notebook.
*** Sample Data Table ***
Laser wavelength (λ)
Trial
nm
Distance to the Wall (L)
Distance between
Central Maximum and
1st Order Maximum (x)
m
Distance between
Central Maximum and
3rd Order Maximum (x)
1
2
Calculations
1. There will be four different calculations:
Use the equation λ= (dx)/(mL) to calculate the distance between slits (d).
Calculation 1: Use (L) from trial 1, (x) for the 1st order maximum (m), and the wavelength of the laser to
calculate d.
Calculation 2: Use (L) from trial 1, (x) for the 3rd order maximum (m), and the wavelength of the laser to
calculate d.
Calculation 3: Use (L) from trial 2, (x) for the 1st order maximum (m), and the wavelength of the laser to
calculate d.
Calculation 4: Use (L) from trial 2, (x) for the 3rd order maximum (m), and the wavelength of the laser to
calculate d.
Place this data in a calculated data table in your lab notebook.
Analyses and Questions
1. What happened to the distance between the maxima when the distance to the screen was increased/decreased?
2. Based on the four calculations for the distance between the slits, how do the values compare to one another?
3. How would the value for the distance between the slits change if the wavelength of the laser was decreased?
4. What are possible reasons for the differences in the calculations for (d)?