Question

In the diagram shown below, a point source O is placed vertically below the center of a circular plane mirror. The light rays starting from the source are reflected from the mirror such that a circular area A on the ground receives light. Now, a glass slab is placed between the mirror and the source O. What will the magnitude of the new area on the ground receiving light? Assume the width of the slab to be very large.

• A. A
• B. Greater than A
• C. Less Than A
• D. Cannot tell, as the information given is insufficient

Answer 1

Answer: (B)

Greater than A

optical path :

When a point object is seen through a glass slab of thickness t, it appears as if it is moved towards glass slab by a distance,$x=t(1-\frac{1}{\mu })$

seeing above formula we came to know that in second case in diagram the source 'O' will appear to somewhat closer to plane mirror so its field of view will be more hence it will spread light more than th first diagram.