Total Internal Reflection : Physics

anpanman SG

A ray of light is incident on one side of a rectangular glass block, so that the angle of refraction is 40 deg in the glass. What is the possible path for the ray, given that the critical angle for glass is 42 deg? Can TIR occur? We do not know the angle of incidence here! Can someone help me?

It is stated that TIR occurs when light rays pass from an optically DENSER mdium to a LESS DENSE medium. However, isn't this a case of less dense to denser medium? (AIR TO GLASS!) My teacher says total internal reflection can occur. Please help, I am really confused.thanks.

What happens to light as it passes from glass into air?

I think that the wavelength increases as speed increases. Why can't we say the frequency has increased?

skythewood SG

TIR can occur

believe your teacher

the light speeds up

when frequency is constant, it won't increase

eagle SG

you can calculate the refractive index from the 42 degrees

Then you can use the refractive index to find the angle of incidence.

TIR can occur from glass to air, but in this question, you will need to sketch out the path ray and calculate the angles. You will find that upon exiting, the angle is 50 degrees, greater than the critical angle of 42 degrees. Hence, TIR will occur.

Less dense to denser, total internal reflection cannot occur at all. Not at all.

What happens to light as it passes from glass into air?

I think that the wavelength increases as speed increases. Why can't we say the frequency has increased?

Frequency is something like a property of the wave... it sort of describes the wave, so it doesn't change.

skythewood SG

hmm.. since teacher is wrong, sack the teacher.

use the equation to stun him.

let angle 2 = 90

anpanman SG

you can calculate the refractive index from the 42 degrees

Then you can use the refractive index to find the angle of incidence.

Less dense to denser, total internal reflection cannot occur at all. Not at all.

Frequency is something like a property of the wave... it sort of describes the wave, so it doesn't change.

So which light ray is the angle of incidence really? the one that first enters the glass block or the lgiht ray which bends upon entering and reflects before leaving the block? i think it is the latter.

skythewood SG

incidence ray has a definition. use it.

anpanman SG

incidence ray has a definition. use it.

i am referring to the angle of incidence which gives rise to TIR. I do not know whether it is the one inside/outside the glass block.

skythewood SG

use your set definition of incident ray.
use definition of refrracted ray.

use the refractive index of n2/n1, n1 being refractive index of medium of incident ray, n2 being refractive index of refracted ray.

use this equation and picture i posted.

critical angle is when refracted angle is 90 degrees.

eagle SG

Incident ray is always the light ray that hits the surface before refraction occurs.

So refractive index is not necessary always equal to sine angle of incidence divided by sine angle of refraction.

eagle SG

i am referring to the angle of incidence which gives rise to TIR. I do not know whether it is the one inside/outside the glass block.

In this case, inside