Question

1. why a rectangular glass slab does not cause Dispersion of white light like prism?
2.under very dim light we are able to see all the object but cannot distinguish between their colours .Explain..

Answer 1

1) A rectangular glass slab doesn't disperse light like a prism because a prism has a large number of surfaces on the inside surface due to its shape whereas a rectangular glass slab is flat and allows light to pass straight through it

2) Yes, Under very dim light we are able to see all the objects but cannot distinguish between their colour because a very less light rays deflect from it towards our eyes which is insufficient to give our rods and cones present on our retina enough sensitivity.

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Answer 2

Hey dear Tapsya...

ANSWER 1----->

☆☆in a Prism, refraction of light takes place at two lateral surfaces .the Dispersion of white light occurs at the first surface of prism where the constituent colour of white light or deviated through different angle .
At second surface of freeze this colour get further separated due to refraction .

☆☆however, in a rectangular glass block ,the refraction of light takes place at two parallel surfaces. although the white light splits into its constituent colours on refraction at the first surface of Glass block, but these colour on suffering reflection at second surface immersed out in the form of a parallel beam, which gives an impression of white light .




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ANSWER 2----->

☆☆In dim light only Rod cells of the retina are sensitive but not the cone cells.
rod cells do not help in differentiating various colours ,means they are not sensitive to colours .

so, in dim light, we just get an idea of the object but not its colour .


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