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**[SOLVED] Internal Reflection Problem**

## Homework Statement

(please check attachment for figure)

ni = 1

nr = 1.48

theta_I = 50 degrees

l = 3.1 mm

w = 42 cm

Find N (Number of reflections before laser beam finally emerges).

## Homework Equations

Snell's Law: ni sin theta_I = nr sin theta_r

## The Attempt at a Solution

My attempt at the solution was to first find angle of refraction, and I found it using Snell's Law.

Theta_r = 30 degrees

Then, if you check the figure I attached, I formed an extension and completed the triangle. Using this, I found angle of incidence.

Theta_I = 90-30 = 60 degrees

Afterwards, I got a triangle of the complete ray. I drew the triangle in the figure I attached. I had Y, which is (l = 3.1 mm). I need to find x, so I used the tangent ratio .

x = (3.1 x 10^-3) tan(60) = 5.4 x 10^-3 m

Then, I used the following ratio:

N= w/x = (42 x 10^-2) / (5.4 x 10^-3) = 77.8

I rounded the value up to get 78. I don't know, but I'm afraid that I might have done a mistake. Can someone please go over my solution and check if I'm correct?

Thanks,

Jin

EDIT: Whilst someone approves my attachment, here's the problem text:

A laser beam traveling in air strikes the midpoint of one

end of a slab of material as shown in Figure 15-24. The

index of refraction of the slab is 1.48. Determine the

number of internal reflections of the laser beam before

it finally emerges from the opposite end of the slab.

#### Attachments

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