Physics - Wave Optics Question with Solution | TestHub

The direction of propagation of light is perpendicular to the wave front and is symmetric about $\mathrm{x},\mathrm{y}$ and z axis.
$\therefore$ Angle made by the light with $\mathrm{x},\mathrm{y}\&\mathrm{z}$ axis is same.
$\therefore \cos \alpha =\cos \beta =\cos \gamma (\alpha ,\beta \&\gamma$ are angle made by light with $\mathrm{x},\mathrm{y}\&\mathrm{z}$ axis respectively)
Also ${\cos }^2\alpha +{\cos }^2\beta +{\cos }^2\gamma =1$ [Sum of direction cosines]
$\therefore \alpha ={\cos }^{-1}\frac{1}{\sqrt{3}}$