Optics, refraction at spherical surface

[Saitama]

Homework Statement

(see attachment)

Homework Equations

The Attempt at a Solution

I don't quite understand the question. It asks the distance of the "unilluminated patch" from the cylinder. There will be only a single point where the rays will intersect. Rest everywhere, it is unilluminated or am I missing something?

Any help is appreciated. Thanks!

 

[tiny-tim]

Hi Pranav-Arora!

Hint: critical angle.

 

[Saitama]

Hi Pranav-Arora!

Hint: critical angle.

Thanks a lot tiny-tim! That solved the problem in an instant.