question_answer

A parallel narrow-beam of light is falling normally on a glass sphere. It will come to a focus

A)  inside the sphere (except at its centre)

B)  on the surface of the sphere

C)  outside the sphere

D)  exactly at the centre of the sphere

Correct Answer: C

Solution :

 Consider a parallel beam of light falling normally on a glass sphere. One of the ray passes undeviated through centre C as shown, other ray AB follows the path ABDI and forms image\[I,\]outside the sphere. \[{{N}_{1}}\]and\[{{N}_{2}}\]are normals to the spherical surfaces.