# Light at Flat/Curved Surface

Hi all,

I am currently reading up on physics in regards to Light, but am still confused as to why

when light goes into a flat surface and comes out from a curved surface, there will be no deflection, and on the other hand

when light goes, first into a curved surface, and comes out from a flat surface, there will be a deflection of light.

can someone kindly explain to me why is this so?

Thanks! :)

It's not whether the surface is curved or flat that matters, but the angle at which the light strikes the surface.
Deflection will occur when the angle (measured to the normal) is greater than zero, irrespective of the shape of the surface.

I've read up further and realised where I was wrong. It seems that only when the light is traveling out from a surface in a direction perpendicular to the surface, would there be no deflection.

However, as I advanced on, I read about total internal reflection but I do not understand how the brightness of the internally reflected light increases as the incident angle passes the critical angle. Could I get some advice on this?

When the light strikes the surface at an angle less than critical, although much of it is refracted and passes through the surface, some light is reflected.
When you pass the critical angle, all the light is reflected.

Interesting! I understand that the refracted ray is much brighter than the reflected ray when the incident angle is less than the critical.

However, when it reaches the critical angle, does the brightness not reach its optimum? I've always had this thought that when the incident angle = critical angle, brightness of internal reflected ray is maximum, and passing the critical angle would affect the brightness again.

If the reflection is "total" it shouldn't matter what the angle of reflexion is. All the light is refelected.