Question

1- What is critical angle in refraction of light?
2-Why do the faces of persons sitting around a camp fire appear to shimmer?
3-Why does the upper surface of water contained in a beaker appear to look silvery?
4-Does the depth of a tank of water appear to change or remain the same when viewed normally from above? If so, why?
5-Can light be "piped" like sound in a doctors stethoscope? Explain.

Answer 1

●●critical angle is the angle which is angle of incidence in denser medium corresponding to which angle of refraction in rarer medium is of 90 degree

●●faces of person sitting around camp fire appear shimmer bcuz of refraction of light.
it means that air around the camp fire is hotter than air around. so light from face of person when travels in hotter medium appears shimmer.

●●the reason is refraction of light

●●depth appears to change bcz of total internal refraction.

●●yes. this is possible

Answer 2

1. Critical angle - The angle of incidence is called critical angle, when  angle   of                                refraction is 90 degree. In this case, total internal reflection                                  takes place and light rays get reflected in the same medium.

2. This is beacuse of the fact that air above the camp fire is hotter than air      around us. So, when the light coming from faces of person sitting around the  campfire passes throught this hot air it gets refracted and as the density of  air is not stable (or optical density) therefore the amount of refraction keeps  on changing due to which the image appears to be shimmering.

3. Here the main phenomenon which takes place os total internal reflection.
   The light from water gets refracted, but the critical angle for water is 49    degrees. So, when these rays hits the surface with an angle more than 48  degrees then total internal reflection takes place. Therefore the upper  surface appears to be silver in colour.

4. No, here refraction dosent takes place as angle of incidence is 0, therefore   no refraction and no refraction means we will see real depth not apparent      depth.

5. Yes, this will happen because the light when passed throught glass rod will internally reflect many times and reach other end. 
For ex in fibre optics.