Question

A hollow lens is made of thin glass and in the shape of a double concave lens. It can be filled with air, water of refractive index 1.33 or CS2 of refractive index 1.6. It will act as a diverging lens if it is (A) filled with air and immersed in water. (B) filled with water and immersed in CS2. (C) filled with air and immersed in CS2. (D) filled with CS2 and immersed in water.

Answer 1

Answer: B)

A hollow double concave lens acts as a diverging lens. When it is filled with a medium of higher refractive index than the surrounding, its diverging power increases.

So if the lens is:

A) Filled with air (n=1) and immersed in water (n=1.33) - Incorrect, air has lower refractive index than water

B) Filled with water (n=1.33) and immersed in CS2 (n=1.6) - Correct, water has lower refractive index than CS2

C) Filled with air (n=1) and immersed in CS2 (n=1.6) - Incorrect, air has lower refractive index than CS2

D) Filled with CS2 (n=1.6) and immersed in water (n=1.33) - Incorrect, CS2 has higher refractive index than water

Therefore, the lens will act as a diverging lens when filled with water and immersed in CS2, which is option B.

The key is that the material inside the lens must have a lower refractive index than the surrounding medium to increase the diverging power of the concave lens.

Step-by-step explanation: