No links please
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{\cos A+\sin \theta }{\sin A}\right)}^2\right\}}^{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}$