Rectilinear propagation of light_physics

Introduction

The French mathematician named Pierre de Fermat discovered this property of light.

Being a kid, we always remember when our teacher used to show us slides on the projector; in the light, we used to make shadows of different animals. This fun thing actually explains a major science phenomenon that is the rectilinear propagation of light, which means that the light travels in a straight line. The source of a light source can be seen only when the path is a straight line between our eyes and the source. Some of the examples from our day-to-day life to understand this are, sun rays entering through a window in a dark room appear to be travelling in a straight line, light emitted through a projector or a laser.

From the introduction we understood that study material of rectilinear propagation of light should include that the light is travelling in a straight line. Whenever we want to represent the propagation of light, we either represent it through a ray or a beam.

Ray can be described as an arrow which shows the direction in which the light is propagated and the diagram representing the same is called a ray diagram.

Beam can be described as a group in which the rays of light are moving in a systematic manner.

Convergent and Divergent beam:

The phenomenon in which the light coming from all different directions meet at a particular point is called a convergent beam of light. To form an image in our retina, the light rays that are travelling from different directions enter into the eye and converge.

The pretty opposite phenomenon, where the light starts from a common point and travels across different directions, is called a divergent beam of light. The headlights of a car show a divergent beam of light.

This phenomenal property of light that travels in a straight line explains a lot of interesting phenomena such as the shadow formation from opaque objects, image formations in pinhole type of camera.

This rectilinear propagation happens in a vacuum or in a medium, which is transparent and uniform.

Let us understand this phenomenon with more real life examples,

Underwater objects:

We are aware that in the same medium the light travels in a rectilinear manner, but what happens when it travels from one medium to another? So a very simple example for this is placing any object under water. In this particular instance, the light travels from a medium of air to the medium of water, the result is that the object looks much smaller in size and also appears to be close. The justification of this incident is that light tends to travel at different speeds in the media which has different densities.

Eclipse:

The two types of eclipses to exist are the solar eclipse and the lunar eclipse. When the solar eclipse takes place the moon comes between our earth and the sun and because of the straight line property of light, the obstruction of light takes place and creates a region of shadow. While in the case of a lunar eclipse, our earth comes in between the sun and moon because of which the light of the straight path, which is travelling towards the moon, gets restricted again resulting in creating a region of shadow.

Different properties of light

• Light is one of the  forms of energy
• Light exhibits dual nature that means it behaves both as a particle and a wave
• In a medium, which is uniform, the light always travels in a straight path, and this is called as rectilinear propagation of light
• It doesn’t necessarily require a medium to travel; it can even travel in a vacuum
• It travels with an intense velocity which is given by 300,000 km/s in vacuum
• When it travels from a rarer to a denser medium, the velocity of light tends to decrease
• All the beautiful colours we see in the sunlight that is through the visible light is just a small part of the electromagnetic spectrum
• The properties of the medium through which it passes doesn’t get altered because of the light

Principle of least time

The consequence of light travelling from point X to point Y in a straight line in the same medium is known as the Fermat’s principle of least time, which means that the light travels in such a way that the time taken to travel is minimum.

Conclusion

The French mathematician named Pierre de Fermat discovered this property of light. The meaning of rectilinear propagation of light is that the light travels in a straight line. It is one of the most important properties of light. Whenever we want to represent the propagation of light, we either represent it through a ray or a beam. This phenomenal property of light that it travels in a straight line explains a lot of interesting phenomena such as the shadow formation from opaque objects, image formations in pinhole type of camera. Eclipses are the best example to understand the rectilinear propagation of light.