Laws of Reflection

Reflection is derived from the Latin word reflectere, re: “back,” and flectere: “to bend,” so it means bending something back. Unless and until any obstacle or second medium arrives in the path of the light ray, the light travels in a straight line. 

Law of Reflection 

The reflection of light by a smooth surface is governed by two basic laws of reflection:

1. The angle of incidence is equal to the angle of reflection.
2. The incident ray, the reflected ray and the normal to the reflecting surface drawn at the interface(point of reflection) of two surfaces all lie in the same plane.

Mathematically, if i is the angle of incidence, AO is the incident ray, O is the point of incidence and OB is the reflected ray, then, i=r

TWO TYPES OF REFLECTION:

1. Regular Reflection
2. Irregular reflection

1. Regular reflection:

This type of reflection takes place when the incident ray is incident on a smooth, shiny surface (eg.plane mirror). If a set of parallel light rays is incident, then after reflection all the light rays will be parallel.

  2.Irregular reflection:

This type of reflection is experienced when the light rays fall on an irregular surface, which is rough and non shiny, for example, the walls of our room.

All rays fall at different points having different relative inclinations. So if we project a beam of light on an irregular surface, all the rays will undergo independent reflection having an unique angle of incidence and hence angle of refraction, accordingly.

It may be noted that although it may seem that irregular reflection is undesirable, it is actually used in theatre screens to reflect the projector rays to a large number of audience, i.e., to scatter the light in all directions.

IMAGE FORMATION:

The incident rays after reflection intersect or appear to intersect and the result is the formation of an image.

There are basically two types of images, real and virtual.

Real Image:

Such an image is formed when the reflected rays actually intersect.

The image formed can be captured on a screen.

It is inverted in nature.

It is produced by a concave mirror and convex lens.

Virtual Image:

Such an image is formed when the reflected rays do not actually intersect but appear to intersect at a point.

Such an image cannot be projected onto a screen.

These images are always upright.

It is produced by a convex mirror and convex lens.

SOME INTERESTING PHENOMENONS OF REFLECTION:

• Total internal reflection:

The phenomenon of complete reflection of light rays into the same medium is called total internal reflection.

It mainly depends on the critical angle (the angle at which the refracted ray is perpendicular to the normal). Once the angle of incidence is greater than the critical angle, the ray is reflected totally instead of getting refracted. 

Generally during scorching heat in the deserts or cold in the oceans, there is a gradual change in the density of air in the atmosphere. A ray passing through the atmosphere undergoes continuous refraction due to the density variation. This leads to a gradual increase in the angle of incidence at subsequent surfaces and after some time, the angle of incidence becomes  greater than the critical angle. This causes the total internal reflection.

Because of this phenomenon we see mirage (illusion) in deserts, and in the oceans we see boats floating in the air.

• Scattering of light

Some light is scattered in all directions when it hits very small debris which include gas molecules or a whole lot of large debris which include dust or droplets of water.

The quantity of scattering relies upon how massive the particle is as compared to the wavelength of mild this is hitting it. Smaller wavelengths are scattered greater.

“Why is the sky blue?” is a common question. Light from the sun is a product of all of the hues of the rainbow. As this light hits the debris of nitrogen and oxygen in our atmosphere, it’s miles scattered in all instructions. Blue light has a smaller wavelength than purple light, so it’s miles scattered a whole lot greater than purple light. When we take a look at the sky, we see all of the locations that the blue light has been scattered from.

Why are sunsets purple? When the Sun seems to decrease withinside the sky, the light that reaches us has already travelled thru lots greater of the atmosphere. This way that a whole lot of the blue light has been scattered out properly earlier than the light arrives at us, so the sky seems redder.

Clouds seem white due to the fact the water droplets are a whole lot larger than the wavelengths of light. For this situation, all wavelengths of light are similarly scattered in all instructions.

Conclusion:

• The angle at which light hits a reflecting surface is called the angle of incidence, and the angle at which light bounces off a reflecting surface is called the angle of reflection.
• The reflection phenomenon is an interface phenomenon.
• TIR being the most important application of reflection is used in optical fibres to transmit signals with minimum loss of intensity.