# Mathematics of refraction of light

1. Jan 18, 2007

### anantchowdhary

Can anyone please prove that if d1=EF and if d2=EG

and angle MEZ=HEF=angle of incidence

and angle HEG = angle of refraction.

Please! can somebody help me prove that d1/d2=refractive index

taking sin i/sin r=refractive index

(The glass slab is ABCD and is kept in vacuum)

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2. Jan 18, 2007

### Staff: Mentor

As you know, you must show your own work in order for us to help you. This seems pretty straightforward using Snell's law and a little trig. Please set up the equations, and we'll see if you are on the right track.

3. Jan 18, 2007

### anantchowdhary

Hey im sorry but with trig im getting some equations but i dont think im on the correct path:

d1=sin i{HF} ....(i)
d2=sin r{HG} .....(ii)

(i) / (ii)

d1/d2=sini.(HG+GF)/sinr(HG)
therefore

d1/d2=mu .(HG+GF)/(HG)

I get stuck after this.Help will be appreciated

4. Jan 18, 2007

### Staff: Mentor

I only looked at it briefly, but I'd start with using cos() since EH is the same for both. I'll try to stop by again later if I can and spend more time looking at it.

EDIT: fixed my typo EF-->EH

5. Jan 18, 2007

### anantchowdhary

after cos how do ii convert it in terms of sin?

6. Jan 18, 2007

### Staff: Mentor

Okay, I'm at home now, and back online for a bit. If you haven't figured it out yet, here are a couple hints.

Since cos() is more useful for describing the physical situation, but Snell's Law is usually written with sin(), then the logical thing to try using would be the combination tan(), right? So start with these:

$$tan(\theta_i) = \frac{sin\theta_i}{cos\theta_i} = \frac{FH}{EH}$$

$$tan(\theta_r) = \frac{sin\theta_r}{cos\theta_r} = \frac{GH}{EH}$$

Try using that to see if that gets you to the solution. BTW, when you look at the drawing of the refracted ray, you see how raising the n will pull in the $$\theta_r$$ and shorten d2? Visualizing what happens as you change a variable in a problem can help you gain the intuition to help you solve problems. In this case, the relationship direction is intuitive, but it takes doing the math to show that the ratio is just the d1/d2 ratio.

7. Jan 19, 2007

### anantchowdhary

Hey im grateful to you for the help provided.But im sorry i just dont seem to get the desired result.Also,

Experimentally i have verified that d1/d2=mu

But im sorry im not able to do it mathematically