Refraction and reflection are two basic properties of light. Clear images can be seen when light bounces off a surface, like in mirrors, a phenomenon known as reflection. On the other hand, refraction occurs as light travels through various materials, bending as its speed changes. This is why things in water appear displaced or bent. In this article, we will discuss example of reflection and refraction.
Reflection & Refraction
The object that emits light is called a light source. Light sources can be of two types—a material that emits light by itself is called a self-emitting source. Like the sun, stars, electric lamp, burning candle, etc. On the other hand, an object that has no light of its own but reflects light from a self-luminous object is called a non-luminous source. Most of the objects around us are inert. Moon and planets are also inert. We see them illuminated because they reflect sunlight.
Reflection of Light: When light passes through one medium and is incident on the surface of another medium, some of the incident light changes direction and returns to the first medium. This phenomenon is called reflection of light.
Refraction of Light: If light passes from one medium to another through the interface between two media, then, in general, the direction of the light ray changes at the interface. This phenomenon is called refraction of light.
Example of Reflection and Refraction
Example of Reflection
- When light falls on a black object, the incident light is not reflected. Black objects absorb incident light almost completely. Hence the inside of optical instruments such as cameras, binoculars, etc. is blackened to prevent unwanted light reflection. White objects, on the other hand, do not absorb any light, reflecting almost all of it. Hence white matter is taken in cases where absorption of light is to be stopped and brightness and colour of reflection are to be kept unchanged. So, the movie screen is whitened.
- Dusk & Dawn: There is light on the surface of the earth until shortly after sunset. This is called twilight. Just after sunset in a region, the sun is below the horizon. So, the sun’s rays can no longer reach that area directly. But the dust in the atmosphere extends far above the surface. Therefore, direct sunlight falls on the dust particles in the upper atmosphere, and scattered reflection of the sunlight spreads the light around. As a result, light enters the surface area and creates dusk. A similar phenomenon occurs shortly before sunrise in some regions. Scattered reflection of the sun’s rays by dust particles floating in the atmosphere causes the light to spread around. So, the darkness in that region of the surface is cut, and the light emerges. It is called Dawn.
- When light strikes a slab of glass, very little of the incident light is reflected—most of the light passes through the pane. So, mirrors are made by coating aluminium on one side of smooth glass panes. This is known as silvering. Because the coating is opaque, almost all of the incident light is regularly reflected from the coating. Very little light is reflected from the surface in front of the pane. Note that earlier silvering was done with silver, later with mercury, but now silvering is done with aluminium.
Examples of Refraction
- Coin Immersed in Water: A coin is placed in a container, and eyes are placed along the edge of the container in such a way that the coin cannot be seen. Now, keep the eyes in that position and fill the container with water to see the coin. When the vessel is empty, the rays from the coin do not reach the eye. As the water is poured, the rays from the coin P are refracted from the dense medium water to the thinner medium air and are deflected away from the perpendicular. The resulting rays appear to diverge from point P’. That is, the virtual reflection of the coin is slightly above the point P’. Obviously, this is the reflection, not the actual coin. Because of this, if a fish is in water with a dense medium for refraction and the thin medium is observed from air, the fish appears slightly higher than its actual position. Therefore, to catch that fish, you have to throw the spear, aiming slightly below the position of the fish.
- A Bar Partially Submerged in Water: Some parts of a straight bar seem to dip diagonally; the bar is bent from the surface. Light rays that come from a part immersed in water pass from a denser medium to a thinner medium. As a result, the refracted rays deviate away from the perpendicular. So, the point A on the rod appears to lie at point B. That is, the submerged part of the shaft seems to have risen slightly. As a result, the reflection of the submerged part of the bar and the reflection of the part of the bar above the water’ are not in the same straight line. Because of this, the rod appears to be bent from the discus.
- Objects and Mediums of Nearly Equal Refractive Index: If an object of nearly the same refractive index is placed through a medium, the object cannot be seen. When the refractive index of the two media is nearly equal, there is almost no reflection of the light rays from their diverging surfaces, and the refraction causes very little change in the direction of the rays. That is, the light rays should move along a straight line. So, the behavior of light does not imply that light is entering from one medium to another—it appears as if the light is moving through the same medium. That is why the division cannot be seen or the existence of division cannot be understood. That is, one medium almost disappears into another medium. For example, the refractive index of glass and glycerin are almost equal, so when a glass rod is immersed in glycerin, the glass rod is almost indistinguishable. So, in such a system, an object appears almost invisible despite the presence of light.
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