What is angle of acceptance?

What is the angle of incidence of a ray if the reflected ray is at an angle of 90^@ to the incident ray ?

What is the angle of incidence of a ray if the reflected ray is at an angle of 90^@ to the incident ray?

A ray strikes the mirror normally, what is the angle of incidence?

The refractive index of a material is sqrt3 . What is the angle of refraction if the unpolarised light is incident on it at the polarising angle of the medium.

What is the sum of the angles of a rectangle ?