Question

A convex lens is made of three different material as shown in figure.
A parallel beam of green light is coming from infinity as shown in
figure. Which of the following option is correct?
n
n
Two bright spots are formed
Three bright spots are formed
One bright spot is formed
No image is formed​

Answer 1

Given:

A convex lens is made up of three different material as shown in the attached diagram. A parallel beam of light is coming from infinity.

To find:

Number of bright spots formed on the principal axis.

Solution:

We know that ; Paraxial rays (from sources at infinity) after getting reflected from a convex lens meet at the focus on the principal axis.

Now, since the lens have been made up with 3 different material, each of these materials have different Refractive Indices.

So, light rays passing through these material will undergo different amount of deviation and three bright spots will be formed on the principal axis.

Each of these spots mark the focus of the corresponding material on the lens.

$\boxed{ \large{ \bold{ \red{no. \: of \: spots} = \blue{3}}}}$