Q. Find the focal length of the projector-lens which projects the image of size $60\times 60$ cm of a slide on a screen 2.4 m away, the slide being of the size $3\times 3$ cm.

Light enters a prism of angle A at a grazing incidence to emerge at an angle $\theta $with the normal. Show that the refractive index of the material of the prism is given by,

$\mu ={\left\{1+{\left(\frac{\mathrm{cos}A+\mathrm{sin}\theta}{\mathrm{sin}A}\right)}^{2}\right\}}^{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}$

What are you looking for?