Refraction Of Light

• Refraction of light
• Refractive index
• Determination of Refractive index
• Total internal reflection
• Critical angle

Refraction of light

Refraction is the bending away of light from the normal as it passes from one medium to the other.

There is a change in the direction and speed of a ray of light when it passes from medium to another medium of different density.  This change in the direction of the light of the light ray which is due to difference in the speed of light in different media is called refraction.

When a ray of light travels from optically less dense medium (air) to an optically dense medium (water, glass), it bends towards the normal.

A ray passing from glass or water to air is bent away from the normal

LAWS OF REFRACTION

1.       The incident ray, refracted ray and the normal at the point of incidence; all lie on the same plane.

2.       The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for a given pair of media.

The second law is known as Snell’s law

REAL AND APPARENT DEPTH

A thick slab of glass appears to be only two –third of its real thickness when viewed vertically from above. Similarly, water in a pond appears to be only three quarters of its real depth. Rays from a coin at the bottom of a bucket of water are refracted away when they leave water and enter the eyes. They appear as if coming from a virtual image, which is apparent depth while the actual depth of the bottom remains and is referred to as real depth

Refractive index=real depth/apparent depth

CLASSWORK 11

1. State the laws of refraction
2. The velocities of light in air and glass are 3.0 x10⁸ m/s and 1.8 x10⁸ m/s respectively. Calculate the sine of the angle of incidence that will produce an angle of refraction of 30⁰ for a ray of light incident on glass

ASSIGNMENT 11

SECTION A

1. The direction of light ray changes as it passes from one medium to the other. The phenomenon is called (a) diffraction (b) reflection (c) dispersion (d) deviation (e) refraction
2. The horizontal floor of a reservoir appears to be 1.0m deep when viewed vertically from above. If the refractive index of water is 1.35, calculate the real depth of the reservoir (a) 2.35m (b) 1.35m (c) 1.00m (d) 0.50m (e) 0.35m
3. Which of the following is an application of refraction (a) eye glasses (b) car headlamp (c) touch light (d) shaving mirror (e) none of the above
4. A ray of light is incident normally on an air-glass interface. What is its angle of refraction (a) 90⁰ (b) 60⁰ (c) 45⁰ (d) 30⁰ (e) 0⁰

SECTION B

• (a) What is:(i) refraction of a wave? (ii) Critical angle?

(b) A water poured into a jar to a depth of 21cm. the bottom of the jar appears to be raised by 3cm when viewed vertically. Calculate the refractive index of the water

• A ray of light incident at an angle of 30⁰ at an air-glass interface (i) draw a ray diagram to show deviation of the ray in glass (ii) determine the angle of deviation