Problem 5.20

A shaft of light passes through a prism with refracting angle \(\theta\) and refractive index \(n .\) Let \(\alpha\) be the diffraction angle of the shaft. Demonstrate that if the shaft of light passes through the prism symmetrically, (a) the angle \(\alpha\) is the least; (b) the relationship between the angles \(\alpha\) and \(\theta\) is defined by Eq. \((5.1 \theta)\)