diffraction grating


Lab Report Structure
1. Aim & objectives of the experiment
 Explain the aim & objectives of the experiment.
2. Introduction
 Mention the experiment.
 Explain the principle of the experiment.
3. Equipment used
 List the equipment you used.
4. Safety
 Did you consider any safety issues while carrying out the
experiment? Explain.
5. Method
 Provide any ray diagrams or diagrams that you used.
 Explain the formula and terms used with appropriate units.
 Explain the procedure.
6. Results
 Include the tables.
 Attach the relevant graphs.
 Show the working for each type of calculation.
7. Uncertainties
 Explain the uncertainty involved in the experiment.
 Error analysis should be provided here.
8. Discussion
 Discuss your result
Relate your findings to the theory.
What result did you expect? What did you get? If you got
unexpected result what went wrong? How it could have been
9. Conclusion
 Give your conclusions.
10.References & Bibliography
 List the references you used (books, websites etc.). Harvard
referencing should be used. Don’t forget the citation. Also, include
all the other sources consulted, even if not directly cited in the
 Read your report and use spell check.
 Do not cut and paste from websites.
 Don’t forget to provide references

About this experiment:
Experiment 1: Diffraction Grating.
Caution. Follow the specific instructions you are given about working safely with laser
You are provided with a laser light source, and two diffraction gratings. One grating has
known line spacing. Task 1 is to use the grating with the known spacing to determine
the wavelength of the laser light. Task 2 is to work out the spacing on the unknown
grating, using the value of λ found in task 1.
For a diffraction grating nλ = dsinθn
where n is the order of the maximum,
λ is the wavelength,
d is the slit spacing of the grating and
θn is the angle between the direction of the central beam and the direction of the
nth maximum.
Task 1
1. Set up the apparatus to produce an interference pattern on the screen.
2. Draw a labelled sketch of your experiment.
3. Indicate, by labels or explanation, how you will obtain n, d, and θn for each
maximum you investigate
4. List the measurements required.
5. Draw a suitable table for your results.
 Include quantities, units and uncertainties in the table headings.
6. Take measurements and record them in the table
7. Plot a suitable graph and use the gradient to find λ.
To find the wavelength of the light
n X (unit) tanθ = x/y θ(unit) sinθ
1 1.4cm 0.035 2.004 0.035
2 2.6cm 0.065 3.719 0.065
3 3.9cm 0.097 5.540 0.096
4 5.2cm 0.13 7.407 0.129
5 6.5cm 0.16 9.090 0.158

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n is the order
y is the distance between the grating and screen
x is the distance between the central maximum and nth maximum
λ = d sinθ /n
{sinθ/n is obtained from the graph}