Draw a labelled ray diagram for the production of pure spectrum.

Compare the focal lengths of a glass lens in the case of red and violet light when the lens is convex.

Compare the focal lengths of a glass lens in the case of red and violet light when the lens is concave.

Is it possible to eliminate dispersion by combining two prisms of different materials but having the same refracting angles? If possible, how?

Describe an arrangement to produce

$\left(\mathrm{a}\right)$  deviation without dispersion and 

Describe an arrangement to produce 

$\left(\mathrm{b}\right)$ dispersion without deviation