# Why light can't penetrate the prism with 45 degree angle

why light can't penetrate the prism with 45 degree angle?

## Answers and Replies

blue_leaf77
Homework Helper
why light can't penetrate the prism with 45 degree angle?
You have to specify other details, otherwise the question becomes invalid because there are many situations in which a light can pass through a 45 degree prism.

Let say, light comes with wide angle like 60 degree of normal of surface and reflect with same angle. there is a formula about that in the web page. why it can't penetrate the prism with wide angle? difference of density between prism and air is a factor, is there another reason for it

blue_leaf77
Homework Helper
Let say, light comes with wide angle like 60 degree of normal of surface and reflect with same angle. there is a formula about that in the web page. why it can't penetrate the prism with wide angle?
That still does not add that much to give a unique solution to the original question. Other details that should be given are the incident angle, the direction of the incoming ray (i.e. from above or below the normal line), and prism material.

it's not a unique question in fact. it's a general question about the situation of light can't penetrate prism and reflect back. one reason is difference of density...

SWATHI N
blue_leaf77
Homework Helper
The way you phrase your question makes it as if no matter what other parameters are, so long as the prism apex angle is 45 degree, any incoming light cannot come out of the prism in the other side. I can have a situation with prism apex angle other than 45 degree but the light cannot penetrate the prism.
one reason is difference of density...
Density of the material? You mean the refractive indices? Then it should also have been stated in the beginning as a condition, along with other parameters which makes the question unambiguous.

nasu
Gold Member
It sure can "penetrate". Look at this case:

You may have in mind something but definitely did not describe it with enough detail.

phinds
phinds
Gold Member
it's not a unique question in fact. it's a general question about the situation of light can't penetrate prism and reflect back. one reason is difference of density...
Yep, it sure is. It is, as others have pointed out, SUCH a general question that it does not have an answer, or looked at differently, it has lots of answers. That's why everyone is pressing you to ask a more specific question that perhaps DOES have an answer.

It sure can "penetrate". Look at this case:

You may have in mind something but definitely did not describe it with enough detail.
Light can penetrate with 0 degree of normal of surface and it is reflected with 45 degree of normal of surface. as it seems in illustration. Density of glass is more than air. I don't ask a specific question about that. my point what is the reason of reflection of light depends on angle of it

In fact, what is called total internal reflection is a phenomenon where some light refracts, not being, then, exactly " total" this reflection.
There appears an evanescent wave at the other side of the prism, which is a patern of intensity that falls exponentially with the distance from the walls of the prism.
Nevertheless, I see that there is space for doubts with respect to the physics of this special case in the chapter of "refraction".

Best wishes,

DaTario

SammyS
Staff Emeritus
Homework Helper
Gold Member
Snell's Law?

blue_leaf77