Measurement of wavelength of light
with diffraction grating

  Date of measure: 04.03.2019 

Tools

optical bench, laser, diffraction grating, ruler, paper

Description of measurement method

Diffraction grating is periodical series of many parallel slits.
If the monofrequent light goes through grating, it forms series of Interference maximum.
Interference maximum is created under angle α.
For interference maximum at diffraction grating equation is:

b. sinα = kλ

b - distance of two closest slits

α - angle under which the maximum is created

k - wavenumber

λ - wavelength

Our measurements:

• We find out distance of two closest slits b

• We light with laser through diffraction grating on paper

•  We measure distance of grating and paper l

• We measure distance x between wavenumber k and wavenumber 0 

• We calculate angle α   ( tgα = x / l )

• We calculate wavelength λ

 Diffraction grating 10 lines in 1mm

 Diffraction grating 20 lines in 1mm

Conclusion:

 Measurement using diffraction grating 10 lines in 1mm

 Measurement using diffraction grating 20 lines in 1mm

Real value of wavelength of red laser pointer

Supplement:

Measurement using diffraction grating 905 lines in 1mm

The End :)