Experiment D2

Question 1

What is the aim of the experiment?

Answer 1

To determine the wavelength of the green line of mercury by measurement of the angular deviation
produced by a diffraction grating.

Question 2

Why is it necessary that the parallel light from the collimator should normally fall onto the diffraction grating?

Answer 2

Because the equation 𝑑sin𝜃m = 𝑚𝜆 is only applicable for only normal incidence.

Question 3

Briefly explain with the aid of sketches how the spectrometer is set up so that the parallel light from the collimator does fall normally onto the grating. (4)

Answer 3

a.) View the slit and rotate the telescope through a measured 90-degree angle
b.) Rotate the table until the reflected image of the slit is seen. Grating is now at a 45-degree angle to the incident beam.
c.)Rotate the table through a 45-degree angle; so that the plane of the grating is normal to the incident beam.