MATHPAL CLASSES & SACHDEVA STUDY ZONE&
CATALYST INSTITUTE
CLASS 10
COLORFUL WORLD
TEXT-1
Glass Prism:
A triangular glass prism is a transparent object made of glass having two
triangular bases and three rectangular lateral surfaces.
These surfaces are inclined to each other. The angle between its two lateral faces is called the angle of the prism.
The rectangular sides of a glass prism are not parallel to each other but the triangular ends are parallel.
Refraction through prisms:
Refraction:
Light not only bounces off surface it gapes through some of them often slowing down and changing direction in the process called refraction. The process of bending of light ray, which is travelling from one medium to another medium is called refraction.
Light ray passing from one medium (air) to another medium bends and travels. It occurs
at the point where light travels from one medium to another of different density.
Example: Pencil immersed in water appears as if it was bent. When you take out the pencil from the water you will not observe any bends.
The light ray coming from the object bends and comes to form an image in our eye, hence will look as if it was bent.
The incoming ray is retracted, and curves towards the normal 1, it is then transmitted through the prism, until it reaches the other surface, and retracted again, away from the normal 2. The end result is always that the ray is deflected away from the apex of the prism.
Any object that has a lower refractive index, then it is called rarer medium.
Any object that has a larger refractive index, then it is called denser medium.
Refraction of light when it moves from denser to rarer medium:
When light passes from a more dense to a less dense substance, (for example passing from water into air), the light is refracted (or bent) away from the normal. (Air - rarer medium, Glass - denser medium)
When light passes from a less dense to a more dense substance, (for example passing from air into water), the light is refracted (or bent} towards the normal in the denser medium. (Air - rarer medium, Glass - denser medium.)
Refraction of Light through Prim:
We can see that a ray of light is entering from air to gla.ss at the first surface AB.
The light ray on refraction has bent towards the normal.
This angle is called the angle of deviation. In this case D is the angle of deviation.
Difference in refraction of light through glass prism and glass slab:
Glass slab has parallel refracting surfaces white a glass prism does not have parallel refracting ssurfaces. Therefore, in case of glass slab, the incident ray emerges parallel to the emergent ray, while in case of prism; the incident ray makes an ang1e with the emergent ray. i.e. angle of deviation. (so, it's not para11e1)
TEXT-2
Dispersion of light:
Newton proved that white light is made up of 7 Colours namely VIBGYOR. He proved it by using a glass prism.
When a beam of white light is passed through a grass prism, it is split up into a band of colours called spectrum. This phenomenon is called dispersion of white light.
The spectrum of white has the colors violet, indigo, blue, green, yellow, orange and red (VIBGYOR}.
The sequence of seven colours obtained from dispersion of white light is called spectrum of white light.
You have seen that white light is dispersed into its seven colour components by a prism. Why do we get these colour? Different colours of light bend through different angles with respect to the incident ray, as they pass through a prism (on refraction). The red light bends the least while the violet the most. Thus the rays of each colour emerge along different paths and thus become distinct. It is the band of distinct colours that we see in a spectrum.
Recombination of the seven colours of the dispersed white light to get white light is known as Recomposition of light.
Formation of Rainbow- Rainbows are generally formed after rains. It is a concentric coloured circular are in the sky when the sun rays Call on rain drops during or after a shower.
The small droplets of rain water which remain suspended in air just after the rains act like a prism. The white light enters from air to water medium.
When white light from the sun enters a spherical raindrop, the light is refracted and dispersed. The different colours of light are bent through different angles.
When different colours of light fall on the back inner surface of the water drop, it (water drop) reflects them (different colours of light) internally (total internal reflection).
The water drop finally retracts the different colours of light again when it comes out of raindrop.
Due to the dispersion of light and internal reflection, different colours reach the
observer’s eye, and the observer can see a rainbow.
Rainbow is formed opposite to the sun. Raindrops act like prism. Rainbow is an example of natural dispersion.
TEXT-3
Atmospheric refraction:
When light my travels from one medium to another, there is bending of the ray.
This happens because the two mediums have different refractive index.
Let us now consider the medium air. Air can be cold as well as hot. When air is hot, its refractive index is less whereas when air is cold, its refractive index is more.
We can thus say that the refractive index of air depends on temperature.
Therefore, during winter, the air is cold therefore refractive index of air will be more and in summer, the air is hot and therefore it’s the refractive index is less.
Therefore, we can say that path of light is bending continuously due to continuous refraction. This is called atmospheric refraction.
Variation of temperature is different at different times. This results in change in path of light at different times.
