Rectilinear Propagation Reflection Of Light

Rectilinear propagation and reflection of light are two important characteristics of light. These are two of the very fundamental concepts in the world of Physics. They tell us how light behaves in different cases and how it reacts to different surfaces. This article covers in detail the rectilinear propagation of light and gives a glimpse of the reflection of light.

Keyterms: Rectilinear Propagation, Reflection Of Light, Rubbertube Experiment, Cardboards Experiment, Ecllipse, Light

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Definition of Rectilinear Propagation Of Light

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The phenomenon of light traveling in a straight line, without any interference, is known as rectilinear propagation of light. A ray of light changes its course only when it enters from one medium to another. Such mediums can be air, glass, water, etc.

Try to stand on the terrace and look around. One will notice that everything around them can be observed. This is possible due to the rectilinear propagation of light. The rectilinear propagation of light can be verified by several simple experiments. The two commonly used experiments are the rubber tube experiment and the cardboards experiment.

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The Rubber Tube Experiment

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The rubber tube experiment is a simple experiment that proves the rectilinear propagation of light. One can carry out this experiment at home with ease.

Requirements

• A flexible rubber tube
• A source of light (a candle, or a bulb, or a lamp)

Procedure

1. Light the source of light and place it on a surface.
2. Take a rubber tube and put its one end in front of the source, at some distance.
3. Make sure that the rubber tube does not have any bends.
4. Place your eye at the other end of the rubber tube.
5. Note your observations.
6. Now, bend the rubber tube at some point along its length.
7. Again, place your eye at the end of the rubber tube.
8. Note your observations

Observations And Conclusion

At the time of first observation, one can see the lit light source clearly from the other end of the rubber tube. This supports the statement that light travels in a straight line. At the time of the second observation, the lit light source is not visible through the bent rubber tube. This happens because the bend in the rubber tube blocks the straight path of light and thus it cannot travel to the end of the rubber tube. This proves that the rectilinear propagation of light is true.

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The Cardboards Experiment

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The cardboards experiment proves the rectilinear propagation of light. One can conduct this experiment at home.

The Cardboards Experiment

Requirements

• A source of light (a candle, or a bulb, or a lamp)
• Cardboards
• A sharp object
• Plain surface (such as table or tiles)

Procedure

1. Light the source of light and place it on a plane surface.
2. Take the cardboards and pierce them together with the sharp object to make an opening at exactly the same spot on all the cardboards.
3. Align these cardboards in front of the light source one after another as shown in the picture.
4. Place your eye near the opening of the last cardboard.
5. Note your observations.
6. Now, move one of the cardboards a little towards the left or right from its original position.
7. Place your eye near the opening of the last cardboard again.
8. Note your observations.

Observations and Conclusion

When the openings of the cardboards were aligned in a straight line, one can observe the source of light from the opening of the last cardboard. This supports the rectilinear propagation of light. But when the alignment of cardboards is disturbed, one cannot see the light source anymore. The change in position of the openings creates a blockage in the path of light resulting in it not moving forward. This proves that light travels only in a straight path.

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Real-Life Examples Of Rectilinear Propagation Of Light

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Rectilinear propagation of light is something people observe on a daily basis. So many illusions around us are created due to the rectilinear propagation of light. A change in the size of objects underwater and eclipses are two of the prominent examples of rectilinear propagation of light in real life.

Underwater Objects

When light passes through water, its medium changes. It goes from air medium to water medium. It is known that light travels in rectilinear motion unless and until it travels through a different medium. Due to this, when an object is placed underwater it looks smaller in size. It also appears to be closer than it is placed. Try this by placing your hand in a bucket of water. It will be observed that the hand appears to be smaller in size and closer to the surface of the water. This is justified by the difference in densities of the two media. Light travels at a different speed in media with different densities.

Eclipse

Two types of eclipses are observed from Earth viz. Solar eclipse and Lunar eclipse. During a solar eclipse, the moon comes between the earth and the sun. Due to the rectilinear propagation of light, light is obstructed because of the presence of the moon. This creates a shadow region. During a lunar eclipse, the earth comes between the sun and the moon. The straight path of light towards the moon is obstructed by the earth, creating a shadow region on the moon.

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Reflection of Light

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Reflection of light is defined as the change in the direction of the path of light on striking a surface. The surface can be regular or irregular. The texture of the surface is irrelevant in the case of the reflection of light. But if you are looking for a clear reflection, the surface should be smooth. A clear image can only be formed with a smooth mirror.

In the above diagram, the reflecting surface is a mirror. Ray P is the incident ray of light. It strikes the mirror at an angle θi. This angle is called the angle of incidence. The incident ray reflects from the mirror. Ray Q is the reflected ray. The ray reflects at an angle θr. It is known as the angle of reflection. Point O is the point of reflection.

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Things to Remember

• The phenomenon of light traveling in a straight line, without any interference, is known as rectilinear propagation of light.
• The rectilinear propagation of light can be verified by the rubber tube experiment and the cardboards experiment.
• Real-life examples of rectilinear propagation of light are a change in the size of objects underwater and eclipses.
• Reflection of light is defined as the change in the direction of the path of light on striking a surface.