2008-07-29

Refraction of Light

Why do you think that part of a spoon that is immersed in water looks bent?


Many people think that as a stick/solid is put in liquid it becomes bent.

Do you think the same?

The reason why the spoon appears to be bent is due to the refraction of light or the bending of light. So we see spoon that appears bent in water or liquid, though in reality it is not.

What is REFRACTION OF LIGHT?

Refraction of light is a ‘bending of the light rays’ phenomena when light passes from one medium to another medium.

Refraction of light occurs when light passes through two transparent media having different densities. There are several consequences when light passes through mediums with different densities and direction.

Rays from Less Dense to Denser Medium

Q: What happens when a light ray passes through of a less dense medium into a denser medium?



A: Light rays will refract towards the normal when passing through a less dense medium into a denser medium, for example from air to glass.


Incidence Angle, Refracted Angle

The angle between the incident ray and the normal is named the angle of incidence, i.

The angle between the refracted ray and the normal is named the angle of refraction, r.



Denser to Less Dense medium

Q: What happens when a light ray passes through a denser medium into a less dense medium?

A: Light rays will refract away from the normal when passing through a denser medium into a less dense medium, for example, from glass to air.



Normal

Q: What happens when a light ray is directed to normal?
A: When light ray (incident ray) is pointed normally on a glass block, the refracted ray is unbent.




The Law of Refraction

The Law of Refraction states that:
(a) the incident ray, the refracted ray and the normal all lie in the same plane.
(b) the ratio of the angle of incidence to the angle of refraction for a given medium is fixed, that is sin i / sin r = constant.

The Law of Refraction is also known as Snell’s Law. (From dutch mathematician, Willebrord Snell)

Snell’s law states that for a light ray that passes from one transparent medium into another, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant.

The Law of Refraction is simplified as follows:
= sin i / sin r = n (a constant)

where
i = angle of incidence
r = angle of refraction
n = refractive index

A formula that is equivalent to Snell’s Law is     n1 sin i = n2 sin r
Where

n1 = refractive index of medium 1
n2 = refractive index of medium 2
i = angle of incidence
r = angle of refraction


The Refractive index

The refractive index is unitless

Here is shown the refractive index for a few materials:

Material            Refractive index
Vacuum            1.000
Air                    1.0003
Water               1.33
Ice                    1.31
Glass                1.53
Paraffin oil        1.40
Diamond          2.40

Refractive index n is defined as:
n = speed of light in medium 1 (vacuum or air) / speed of light in medium 2

Refractive index can also be represented by the following equation, Snell’s law:
n = sine of the angle of incidence, sin i /sine of the angle of refraction, sin r ( n = sin i / sin r)

Refractive index can also be determined by using:
n = Real depth, H /Apparent depth, h ( n = H/h)

Phenomena Due to Refraction of Light

The apparent Depth – A swimming Pool Looks Shallower than it Really is.

A Straight Object Placed in Water Looks Bent at the Surface (as discussed in the beginning).

Formation of Rainbow

Many more.... All the best!

7 comments:

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