A beam of light enters a block of flint glass (n = 1.65) at a 24 degree degree a

Question

A beam of light enters a block of flint glass (n = 1.65) at a 24 degree degree angle from the normal, as illustrated. Calculate the path the light takes until it leaves the glass. Don't worry about the exact position, but assume the illustration is reasonably accurate. Calculate the exact angles the light travels at each time it refracts or reflects (you have to figure out which it does), and remember that the normal for the side of the glass block is perpendicular to the normal for the top of the glass block. Finally, assume all the corners of the glass block are right angles.

Explanation / Answer

Refracting angle at shown face= 14.24 degree

This is obtained by Snell's law.

Refracting index= sine of angle of incidence/ sine of angle of refraction

Now, for total internal reflection

Refractive index = 1/sin C

Where C is critical angle

C= 37.3 degrees

Now, single of incidence at the adjacent face=90-14.24= 75.76 degrees (using simple geometry)

So, total internal reflection takes place

Angle of incidence on third face is 14.24 degrees . So the ray comes out of the 3rd face at an angle 24 degree (symmetry)

This is the path of light

It enters the first face, suffers refraction then, at 2nd face adjacent to the 1st face it suffers Total internal reflection

Finally it comes our at 3rd face after refraction. The emergent ray is parallel to the incident ray.

To calculate the exact path length

Dimension of the glass has to be given.

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