Light

byRifki Irawan

Refraction

Based on how the light behaves as it encounters a substance, substances can be classified into:

• Transparent substance is one through which you can see clearly.There is no substance known that is perfectly transparent, but many substances are nearly so; example : glass or water

• Opaque is substances that are unable to transmit any light.Opaque is the most visible substance among others; example : stone or wood

• Translucent is a material through which some light rays can pass, but through which objects cannot be seen clearly because the rays are diffused.Translucent substances are made for special purposes; example : plastic

incident ray

refracted ray

i

r

normal

air

glass

When light travels from air into glass of water, its speed decrease.

A medium is said to be optically dense if its slows down the speed of light.

A ray of light bends towards the normal when it enters an optically denser medium at an angle.

Refraction

The bending of light as it moves from one medium to another. It is due to the difference in speeds of light in the two media.

incident ray

refracted ray

i

r

normal

air

glass

When light travels from glass of water into air, its speed increase.

A medium is said to be optically less dense if its speed up the speed of light.

A ray of light bends away from the normal when it enters an optically less dense medium at an angle.

Laws of Refraction (Snell’s Law)1. The incident ray, the refracted ray and the normal at the point

of incidence all lie in the same plane.2. For two given media, the ratio is a constant, where i is

the angle of incidence and r is the angle of refraction.

sin i

sin r

sin i

sin ralso known as the refractive index (n)

the refractive index (n) of a medium may also be defined as the ratio of the speed of light in vacuum to the speed of light in that medium

n = speed of light in vacuum (or air)

speed of light in medium

n = speed of light in vacuum (or air)

speed of light in medium

c

v=

1. If the speed of light in air is 3.0 x 108 m • s-1 , find the speed of light in diamond of refractive index 2.42

2. A material has a refractive index of 1.7. A ray of light at an incident angle of 30 o enters the material. Calculate the angle of refraction.

3. A ray of light at an incident angle of 45 o. Its refraction angle is 60 o. Find its refractive index.

4. A light is refracted on the glass by the angle of incident 40 o. If the speed of light in air is 3.0 x 108 m • s-1 . And the speed of light in the glass is 2.0 x 108 m • s-1 . Calculate the angle of refraction.

Example :