A large block of plastic is solid except for an air-filled void in the center of the block. The void is

in the shape of a double concave lens. A ray of light traveling parallel, but slightly above or below

the central axis of the "lens" will:

A. emerge parallel to the axis because the index of refraction of the lens is smaller than that of

the surrounding plastic medium.

B. be bent away from the axis because the void acts like a converging lens.

C. be bent toward the axis because the void acts like a diverging lens.

D. be bent toward the axis because the void acts like a converging lens.

E. be bent away from the axis because the void acts like a diverging lens

The answer is D but I am not sure how.

When a converging lens made of glass is placed in a medium having refractive index more than glass, the converging lens becomes diverging in nature. Similarly when a diverging lens made of glass is placed in a medium having refractive index more than glass, the diverging lens becomes converging in nature.

In the given case plastic has refractive index more than air. The concave lens (diverging in nature) is made of air. Since medium surrounding the lens has greater refractive index then the nature of lens gets reversed.

In this case, diverging lens made of air becomes converging in nature.

So the rays will be bent toward the axis because the void acts like a converging lens.

Option D is correct.