Question

1. What is total internal reflection and why is it important in optical fibers? What is the critical angle?

2. Does a diverging lens have a focus point?

3. What type of lens, diverging or converging, would you use for a magnifying glass? Explain.

Answer 1

1. Whenever a ray passes from denser to rarer medium at an angle greater than critical angle, instead of being refracted it undergo reflection and returns in same medium which is known as Total Internal Reflection.

In optic fiber, the fibers are made of glass and covered with some material (cladding) whose refractive index is lower that glass. Now when we pass light from one end at an angle greater than critical angle then the light undergo Total Internal Reflection within the glass and is not able to leave the glass, as a result the light traces the glass Parth by undergoing several total internal reflections.

Critical angle is that angle at which if a light is sent from denser to rarer medium the angle of refraction becomes 90 degrees or the light runs parallel to the surface. Mathematically:

2. The focal point of a concave lens is the point where light rays parallel to the axis seem to diverge from after passing through the lens. So, yes concave lens do have focus point.

3. The lens used in magnifying glass are convex lens. They are used because when an object is placed between optic center and focal length of the lens the image formed is erect and magnified.