Totally internally reflected

**gbenguse78** · January 12th 2011, 04:33 AM

Hi
I am looking for a good website. I need practice with drawing refracted rays and totally internally refracted rays. This will also include critical angles.

Please recommend any useful websites. It will be wonderfully appreciated. The exam is on Monday.

Thanks.

**mr fantastic** · January 12th 2011, 12:43 PM

Originally Posted by gbenguse78

Hi
I am looking for a good website. I need practice with drawing refracted rays and totally internally refracted rays. This will also include critical angles.

Please recommend any useful websites. It will be wonderfully appreciated. The exam is on Monday.

Thanks.

Did you try using Google?

**gbenguse78** · January 12th 2011, 11:57 PM

Yes. Most of the websites are information based. I have the textbook' Nelson' Physics and their is not much information on how to draw them. I have also considered the past questions and the answers are written, not demonstrated. So, at a loss really. Its very difficult because I study independently.

**Unknown008** · January 13th 2011, 01:02 AM

If it's drawing, you should know how to precisely draw any angle given the normal and the reflecting/refractive surface, knowing where the light will bend the more when refraction is concerned.

The critical angle is often required for you to work out, given the incident angle and the refractive index between the two media involved.

You could post some of your questions (one at a time) and post what you tried to do. We'll help you know whether you are correct or not, what you have to change/improve, etc.

**gbenguse78** · January 13th 2011, 03:33 AM

Thanks. I dont know how to sketch on the forum. How do I do that?

**Unknown008** · January 13th 2011, 05:56 AM

Hm... the simplest way to do this is to have your sketch as an image (scanned, or created through paint of another graphic program you are familiar with). If you can have grids in your image, they'll greatly help. Then you upload it on the site and attach it to your posts, or you upload it on an image hosting site and post the link. If on top of that you can measure angles, it'll be awesome!

**e^(i*pi)** · January 13th 2011, 06:28 AM

When it comes to total internal reflection and refraction then you'd do well to remember Snell's Law

$n_1 \sin\theta _i = n_2 \sin\theta _r$ where:

$n_1$ = Refractive index of the incident material (the material it's leaving)
$n_2$ = Refractive index of the material it's entering
$\theta _i$ = incident angle
$\theta _r$ = refracted angle

The critical angle is when $\theta _r = \frac{\pi}{2} = 90^{\circ}$

$\theta _c = \arcsin \left(\dfrac{n_2}{n_1}\right)$

For incident values above this total internal reflection occurs (and it's always the same angle as the incident so you draw a perpendicular and sketch the same angle)

**mr fantastic** · January 13th 2011, 06:49 AM

Originally Posted by e^(i*pi)

When it comes to total internal reflection and refraction then you'd do well to remember Snell's Law

$n_1 \sin\theta _i = n_2 \sin\theta _r$ where:

$n_1$ = Refractive index of the incident material (the material it's leaving)
$n_2$ = Refractive index of the material it's entering
$\theta _i$ = incident angle
$\theta _r$ = refracted angle

The critical angle is when $\theta _r = \frac{\pi}{2} = 90^{\circ}$

$\theta _c = \arcsin \left(\dfrac{n_2}{n_1}\right)$

For incident values above this total internal reflection occurs (and it's always the same angle as the incident so you draw a perpendicular and sketch the same angle)

All of which is readily found using Google (which was the point of post #2).

Originally Posted by gbenguse78

Yes. Most of the websites are information based. I have the textbook' Nelson' Physics and their is not much information on how to draw them. I have also considered the past questions and the answers are written, not demonstrated. So, at a loss really. Its very difficult because I study independently.

There is plenty to be found using Google!! And you can always refer to other textbooks (library is a good start).

**snowtea** · January 13th 2011, 07:48 AM

First page found by Google typing "reflection refraction flash"

Reflection and Refraction

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