NCERT Solution for Class 10 Science Chapter 11 Human Eye and Colourful World
What is meant by power of accommodation of the eye?
The images of objects at different distances from the eye are brought to focus on retina by changing the focal length of the eyelens. This is known as power of accommodation of the eye.
What is the near point and the far point of a normal human eye?
Near point is 25 cm and far point is infinity.
Why is a normal eye not able to see clearly the objects placed closer than 25 cm?
A normal eye is not able to see clearly the objects placed closer than 25 cm because thefocal length of eyelens cannot be decreased below a certain minimum limit.
What happens to the image distance in the eye when we increase the distance of an object from the eye?
In order to focus the eye on objects situated at varying distances, the focal length of the eye lens is changed by the action of ciliary muscles.
Explain why the planets do not twinkle.
Planets are comparatively much closer to the earth and are thus seen as extended sources of light. Being of larger size, planets can be taken as a collection of a number of point-sized sources of light which nullify the twinkling effect of each other.
Why does the sun appear reddish early in the morning?
At the time of shnrise, the rays of the sun have to travel a larger atmospheric distance. As the wavelength of red colour is the largest of all the colours of sunlight, most of the blue colour and other colours are scattered away. Only red . colour which is,,least scattered, enters into our eyes. Hence, the sun appears reddish at the time of sunrise.
Why does the sky appear dark instead of blue to an astronaut?
This is because there is no scattering of light due to the absence of atmosphere in the free space.
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