
Experiment to estimate
the wavelength of the light given by a sodium lamp
1.
Preparation: 
a) 
Read
about continuous spectra and line spectra. 

b) 
Revise the work
about diffraction gratings (especially the equation relating
distance between gratings to angular position of diffracted
image). 

c) 
See part
3 below. 
2. 
Use a
diffraction grating as shown in the diagram below. 



One person looks
through the diffraction grating while the other person places a
thin rod so that its position coincides with the observer's view
of one of the diffracted images of the slit. Mark the positions
of as many images as can be seen. From the diagram it can be
seen that the angle to be measured is given by 

q
= tan^{1}(x /
)

3. 
Calculate the maximum number of
diffracted images theoretically produced by the
diffraction gratings available. When you do the experiment, you
will not be able to see as many images as your calculations
suggest. Why not? 

