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| Image: pixabay |
As you study light, it continuously sparks curiosity. This light is, in a way, the reason we perceive the present moment. Light has no inherent "weight" or "mass." The light that leaves the Sun takes about eight minutes to reach the Earth. Therefore, the Sun we see is actually the Sun as it was eight minutes ago. If the Sun were to explode now, it would take eight minutes for us to be aware of it.
While studying light, we can learn many fascinating facts like these. For example, why does the light that strikes a glass surface reflect only in one particular path? What is the reason for this? Also, when light deviates, why does it travel along only one specific path as it refracts? Would you like to find out the answers to these questions?
First we need to know about light reflection and refraction.
The light that falls on an object, returns from the object in the same manner (without penetrating through the object), is called reflection.
In other words, every color in the light, as it reaches the object, must also leave the object in the same manner. An example of this can be seen in a mirror that reflects our face. The colors that reflect off our face and reach the mirror, return unchanged, allowing us to see our face.
A white paper reflects all the light that falls on it. However, we cannot see our face in the white paper because the reflected light rays are scattered in all directions (non-polarized) instead of being organized in a uniform direction.
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| Image: wikimedia commons |
Refraction is the change in the path of a light ray when it passes through two media of different densities.
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| Image: wikimedia commons |
A ray of light incident on a mirror reflects only in a certain direction. The reason for this is as below...
Path of light in reflection:
The mathematician Pierre de Fermat was the first to discover which paths a light ray takes in refraction and reflection .
According to him, a ray of light chooses the path which can be reflected in the shortest time.
See the image below
In this diagram, the light ray originating from point A, strikes a mirror and reflects, reaching point B. The light ray may also reach point B through different paths, but there is a reason why the ray in this diagram chooses the path shown.
As we mentioned earlier, a light ray will choose the path that allows it to reflect in the shortest time. Moreover, for us to see the light reflecting, the angle of incidence (θi) at which the light strikes the mirror and the angle of reflection (θR) must be equal.
Only when the angle of incidence and the angle of reflection are equal on the mirror can we see our reflection. However, in a white paper, the angle of incidence and the angle of reflection are not equal, which is why the paper does not reflect the light.
There is a method to determine along which path the light reflects. First, as shown in the diagram above, draw a perpendicular line from point A to the mirror. Then, at the same distance between point A and the mirror, mark a point A¹ along the perpendicular line. Next, draw a straight line that connects point A¹ and point O, where the light strikes the mirror.
The line thus drawn will represent the path along which the light will reflect. Here, the angle of incidence and the angle of reflection will be equal.
θi=θR
Path of light in refraction:
Now let's come to refraction. When light travels from a less dense medium to a more dense medium, or from a more dense medium to a less dense medium, it is reflected.
But how does one deviate?
A ray of light traveling from a medium of less density (air) to a medium of higher density (water) moves towards a vertical line drawn from a plane separating the two media.
Similarly, when a ray of light moves from a medium of higher density to a medium of lower density, it deviates from that vertical line. To understand this, take a close look at the image below.
