What do you Mean by the Reflection of Light?

When a light ray (termed as the incident ray) hits a surface and bounces back (forms a reflected ray), the process of reflection of light has taken place.

This scientific process has various real-life practical applications which we are going to look at in this unit. This comes under the section of optic physics.

Reflection in Plane Mirrors

Plane mirrors are found easily in our daily life. It is the normal flat mirror we use every day which is polished on one side so that it can reflect light. 

In the case of plane mirrors, they easily reflect light and the angle of reflection is equal to the angle on incidence.

The images formed by plane mirrors are always virtual and are of the same size as the object. One major feature is that the image is laterally inverted. So, if you raise your right hand the image on the mirror will show the left hand being held upwards.

Other than the general use of plane mirrors, they are also used to construct devices.

Periscope is made of plane mirrors. This instrument is used to see over objects. It is used in submarines to look above the water surface and also in double-decker buses. It is made up of two plane mirrors that are set parallel to each other at each corner of a long tube. It is at an angle of 45 degrees to the incident light rays.

A kaleidoscope is a device that produces colorful designs and patterns using the mechanism of reflection. It is made up of a tube of plane mirrors that is sealed at one end. The tube can be of different shapes. Later colorful beads are placed in the tube. The observer looks through one end of the tube and light reflects off the numerous mirrors in the tube. As the tube is rotated the movement of the beads gives the viewer varying colors and patterns in the design. This instrument is used by designers to yield wallpaper designs.

Reflection in Concave Mirrors

Concave mirrors are a type of spherical mirror that has curved surfaces and is painted on the outer side. This becomes an inner surface reflecting mechanism. Light converges at a point when it first strikes the surface and then is reflected.

In a concave mirror, if it has a long focal length (the distance of the object must be less than the focal length) the image produced is magnified.

This theory is put into practical use for the making of makeup mirrors, which requires a magnified version of the incident image. On the same lines is the making of the dentist’s mirrors to magnify the image of the teeth so it is seen clearly.

It is also used to make an illusion box. It is a device that can produce a virtual object. It is a box with a concave mirror inside it. The inner surface of the box is painted black to create a dark environment. The object and light source are towards the bottom as shown in the image. This creates an illusion when it is viewed by the observer in a dark room with the light source switched on. The illusion is that the object seems to be hanging in space inside the box. If someone tries to touch the image they see, he or she will not be able to do so as the object is not placed at that place.

Reflection in Convex Mirrors

 Convex mirrors are spherical mirrors that have curved surfaces but unlike concave, the inner side is painted and not the outside. So, this has an outer surface reflecting mechanism. This type of mirror diverges light when it strikes the reflecting surface.

The images formed are always virtual, erect, and diminished.

Side wing mirrors and rear-view mirrors of a car use convex mirrors. This is because the diminished image formed gives the driver a larger field of view than the normal human eye. Helps the driver have a better check on the road and traffic behind.

It is also used in driving mirrors and shop security mirrors as it gives the viewer a wider view than normal. Moreover, it serves as an advantage to view blind corners on the road – blind corner mirrors. It helps in road safety by being able to view the traffic around sharp corners. 

They are also used in eyeglasses. This is because convex lenses can be used for correcting farsightedness. Farsightedness occurs when the distance between the eye's lens and the retina becomes too short. As a result of which the focal point now lies behind the retina. So the convex lens in eyeglasses increases refraction which accordingly reduces the focal point.

Total Internal Reflection

Refraction is a process of transfer of light rays from a more optically denser medium to a less dense medium. But when the angle of incidence is greater than the critical angle of the medium, instead of undergoing refraction the light ray gets reflected into the same medium. This is called total internal reflection. It is the continuous bouncing of incident light rays. This allows you to view the inside of objects.

This is concept is put into use in optical fibers that are used in medical treatments to see the inside of the body of patients and in telecommunications to pass signals. They are used in internet cables because of their advantage to transmit data at great speeds.

Reflection in Parabolic Mirrors

It is a concave mirror whose cross-sectional area is shaped like the tip of a parabola.

They are used to gather light in reflecting surfaces and project a beam of light rays. This is why it is used in torches and car headlamps. A small lamp is kept at the focus point of the concave mirror so that parallel rays of light are produced.

Also, parabolic antennas are used for high-energy point-to-point communication. 

Retroreflector

It is a device that reflects the light waves to its source along the same light direction with minimal scattering.

This mechanism is used on roads, road signs vehicles, and special safety clothing. It is the yellow strip we see at the sides of roads, especially on mountainous routes. When the headlights of a car illuminate light towards the retroreflective surface, the light is directed back directly towards the driver. It is seen in the dark only if there is a light source between the viewer and the reflecting surface.  A similar mechanism is used for the road signs.

Further, it is recommended by the safety department to be used on all emergency gear, ships, and boats. This makes it easier to spot at night.

Moreover, similar types of retroreflectors have been placed on the moon and mars.

Similar Topics

• Converging lens
• Diverging lens
• Mirrors and lenses 

Context and Applications

This topic is studied in

• Bachelors in Science (Physics)
• Class 10^th, 11^th, and 12^th