PRISM

Question 1

what is a prism?

Answer 1

• A Prism is a transparent medium bounded by five plane surfaces with a triangular cross section.
• Two opposite surfaces of a prism are identical and parallel triangles.
• The other three surfaces are rectangular and inclined on each other.

Question 2

How does Refraction occur through a prism?

Answer 2

A ray of light of a single colour falls obliquely on one of the faces of the prism.
- This ray enters from the air to the glass (i.e from a rarer medium to a denser medium) and so it bends towards the normal and thus it gets refracted.
- This refracted ray now enters from glass to air (i.e from a denser to a rarer medium) and so it bends away from the normal and travels along the opposite face through which it entered.
- This ray on passing through a prism the light ray bends toward the base of the prism.

Question 3

What is the difference between the emergent ray obtained by a prism and the emergent ray obtained by a rectangular glass block?

Answer 3

• The emergent ray through a prism is not in the direction of the incident ray but it bends towards the base of the prism because refraction occurs at two inclined surfaces.
• In a rectangular glass block, refraction of light occurs at two parallel surfaces so the emergent ray is in the direction of the incident ray

Question 4

What experiment did Newton do with white light?

Answer 4

Newton allowed white light to enter a dark room through a small aperture in a window and placed a glass prism in the path of the light rays.
The light coming out from the prism was received on a white screen.
On the white screen a coloured patch like a rainbow was obtained. This coloured patched is known as a spectrum.

Question 5

What is a spectrum?

Answer 5

Spectrum is the coloured band obtained on a white screen on passing white light through a prism. The order of the coloured band (VIBGYOR) starts from the side of the base of the prism

Question 6

What is dispersion of light?

Answer 6

If white light is passed through a prism, it splits into different colours. This is called the dispersion of light.

Question 7

State the cause of dispersion of light

Answer 7

The cause of the dispersion of light is:
- The speed of light of all colours is the same in air and water but differs in a transparent medium such as glass.
- Refraction of light
- the refractive index of a transparent medium is different for lights of different colours

Question 8

State the colours with Max and min speed in a transparent medium

Answer 8

Max speed is red light
Min speed is violet light

Question 9

How is the rainbow formed?

Answer 9

In the rainy season, sometimes after the rain we get to see a rainbow just opposite the sun.
It is due to dispersion of sunlight by rain drops in the atmosphere which behaves as small prisms