Rectilinear Propagation of Light

One of the most fundamental concepts in physics, it is important for science students to understand what is rectilinear propagation of light. It has been described below in vivid details, along with relevant examples.

Rectilinear propagation of light refers to the propensity of light to travel along a straight line without any interference in its trajectory. When light travels through a medium, say air or water, it follows a straight line. However, the path only changes in case there is a shift in the medium. 

For instance, if a ray of light passes from air to water, the path of light bends based on the change of density. You must note, this phenomenon is known as refraction. Another example of rectilinear propagation of light involves the formation of shadows. When you place an object in front of a candle, you will see its shadows on the wall. It is because light travels along a straight line and leaves only the areas where the object interferes. 

What is Meant by Rectilinear Propagation of Light? 

A simple example will help you understand the concept if you intend on learning what is meant by rectilinear propagation of light. 

However, you will need the following items to help this simple experiment succeed – 

  • A flexible rubber straw or plastic tube which measures around 10 inches. 

  • A lit candle, or a lamp, or a bulb. For your ease, any strong source of light will work for this experiment. 

Follow the steps given below to understand how rectilinear propagation of light function in real life – 

  • You have to point one end of the rubber straw or the plastic tube at the source of light. Then maintain some distance from the source and hold the material still without any disturbances. 

  • Put your eyes on the other end of the tube. You will see the source of light, such as a candle or a lamp, through the tube. 

  • For the third step, bend the rubber tube and try to look through it. This time, you will fail to see the source of light in that position. 

Understanding how to define rectilinear propagation of light, you must note that light always travels along a straight line. As a result, you could not see the source of light once you bent the tube. This very principle also helps in the formation of shadows when you hold an object in the path between the light source and a wall. 

However, you have to use an opaque object instead of transparent or translucent material. An opaque object refers to a material that prevents light from passing through it. For instance, light cannot even pass through a book or a cricket bat. 

On the other hand, light easily makes its way in a straight line through glass or a thin piece of cloth. In this case, you can refer to these articles as transparent and translucent, respectively. 

How to Understand the Rectilinear Propagation of Light Further? 

For your better understanding of this interesting concept, let us give two examples of rectilinear propagation of light that take place in real life. 

  • Eclipse – Eclipse is a phenomenon when a celestial body such as Earth comes in the path of light originating from the sun and reaching the moon. In the case of a lunar eclipse, you can see the shadow of our planet on the moon.  However, this happens only as long as it continues to be in the path of sunlight. 

  • Shorter Hands Under Water – When you submerge your hand under water, you will see that it appears shorter and closer. It is because the light that your hand reflects travels in a straight line underwater, but changes its original course when in air. It is because air and water have different densities and light travels at different speeds because of it. This phenomenon makes your hand appear shorter and closer. 

This is the briefest possible explanation of rectilinear propagation of light for class 7 students. However, if you are a big science enthusiast, stay on our page for more interesting information. You can also download our Vedantu app for a personalized learning experience. 

FAQ (Frequently Asked Questions)

1. What is the Rectilinear Propagation of Light? 

Ans. Rectilinear propagation of light refers to the tendency of light to travel along a straight line. 

2. What is a Real-Life Example of This Phenomenon? 

Ans. Solar or lunar eclipses are the real-life examples of rectilinear propagation of light. 

3. When Does the Path of Light Bend? 

Ans. The path of light bends when it travels from one medium to another medium, with the latter having a different density.