Page 168 - Science Class 08

other end. Clearly, the red colour at the other When the spectrum of light was made to pass
end of the band has the longest wave-length. through the second prism, a beam of white

Two invisible colours are also there in this band light emerged out of it on the other side. If
of refracted light, one at each end. They are confirmed the fact that white light is made up
ultraviolet at one end and the infrared at the of seven visible colours.
other end. So, they remain invisible to the eye. Remember that, the colours of the spectrum

Sir Isaac Newton was the first scien st to always appear in the same order. We can see
obtain a spectrum of sunlight through a prism. these colours in the rainbow where raindrops
He used a second prism to diverse the hanging in the air act as prisms to cause the
spectrum further. But no such thing happened. rainbow. One more thing, it is difficult to
So, he made a new experiment placing a pinpoint boundaries of the colours of the
second prism opposite to the first prism. pa ern, yet the colours can be dis nguished
from one another easily with the naked eyes.

OPTICAL ILLUSION
If we look down a long straight road, it looks
growing narrower in the distance. Trees and
poles on both sides of the road look growing

smaller too.
A person wearing a dress with ver cal stripes
looks thin and tall while that wearing a dress
with horizontal stripes looks shorter and stocky.
Sir Issac Newton experimen ng with prism.

Normal : The peculiar drawn at the point where a ray strikes an object
Incident ray : Light-ray that strikes a medium before entering it

Refracted ray : Light-ray that gets deflected while entering a new medium
Medium : Material through which light or heat energy travels
Refractive index : Ratio of light-velocity in one medium to this velocity in another

Let's RLet's RLet's RLet's R
Let's R
Let's Revise evise evise evise evise evise evise
Let's R
i Refraction of light means deflection of its rays from their straight path.
i Speed of light differs in various mediums – faster in rarer mediums and slower in denser ones.
i The ratio of the velocities of light in two different mediums is the refractive index of the
second medium.

i A light-ray after refracting through a glass slab emerges parallel to itself, but in a laterally
displaced position.

i Colours of white light merge into one another to form white light on passing through a prism
placed in the opposite position.

168 Science-8