Aim: To determine the wavelength of Laser using one dimensional diffraction grating.

Apparatus used in the experiment: Laser, one dimensional diffraction grating, ruler, screen.

Apparatus to be used by you: 15cm or 30cm ruler.




d = grating element,

n = order of maxima,

θ = angle between central maxima and first order maxima ,

λ = wavelength of laser


  • Setup for the experiment is as given below.
  • Laser is focused on the screen and grating is placed between the laser source and screen.
  • The photographs of diffraction pattern for different distances between the screen and the grating are given below.
  • The distance between the grating and the screen, D is mentioned on each photograph, which can be seen by magnifying the photograph.
  • Generate the data with 1% uncertainty in the measurement, from the photographs above.
  • Plot a suitable graph and determine the wavelength of laser only from the slope of the graph.
  • The grating used in the experiment has 12868 lines/inches.

Click below to download high resolution images (if needed):


In order to get your response, we are providing you with a google form. So that, we can get an idea about

  1. your data collection techniques,
  2. variables chosen for measurements,
  3. your data and
  4. the graphs that you will plot.

The google form: https://docs.google.com/forms/d/1LkTVewvaICMcGZBV__vBta59x6j2IIC5sFdiNBCzZCM/edi

Use the spreadsheet for calculations if needed: spreadsheet

You may download the graph sheet to plot the graph: Graph Sheet


What is meant by 1% uncertainty in the measurement of data?

When we say that we want to measure a variable, y with 1% uncertainty, it means that

It means that the measured quantity is at least 100 times the least count.

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