Question

An isosceles right-angled prism and a convex lens (focal length $=40cm$) are placed as shown in the above figure, and a 5 cm wide strip with the letter 'LIGHT' written on it placed as indicated. What is the nature and position of the image formed after refraction through the prism and the lens?

[Given the critical angle of the glass used for the prism and the lens is ${42}^{\circ }$.]

Answer 1

Since the critical angle of glass is $42°$(given). So,we will be observing total internal reflection. Now we will be observing inverted image in the prism at same disrance in parallel to the lens.

Hence the object distance from the lens i.e image of the prism will be $67+13cm$ i.e $80cm$ and since $f=40cm$ then $2f=80cm$. Hence $u=2f=80cm$ so the image will be formed inverted of the image in the prism. So the nature of final image will be of the same size, real image & it will be erect.