Human Eye and Colorful world important questions

A. i) The eye lens can form clear image on the retina when an object is placed between far point and point of least dis- tance of distinct vision.

ii) If we are able to being the image of the object kept beyond far point, between the far point and point of least distance of distinct vision using a lens, this image acts as an object for the eye lens. 

iii) This can be made possible only when a concave lens is used.

A. i) Eye lens can form a clear image on the retina when any object is placed beyond near point.

ii) To correct the defect of hypermetropia, we

need to use a lens which forms an image of an object beyond near point. When the object is between near point (H) and least distance of distinct vision (L). 

iii) This is possible only when a double convex lens is used.

A. i) The rainbow is a spectrum of sunlight in nature.

ii) The rainbow is formed due to the dispe- rsion of sunlight by water droplets suspen- ded in the atmosphere after rainfall.

iii) This phenomenon is due to the com- bination of the refraction of sunlight by spherical water droplets. Which act as prisms and internal reflection occurs. 

iv) Parallel beams of light coming from sun getting dispersed at different angles of deviation produce a cone of rays at the observer's eye.

v) Therefore the rainbow appears as an arc a circle for an observer on the earth.

4. Explain briefly the reason for the blue of the sky.

A. i) Scattering of sunlight through molecules of atmosphere is the reason for the blue of the sky.

ii) Our atmosphere contains atoms and molecules of different sizes.

iii) According to their sizes they are able to scatter different wavelength of light. 

iv) For example the size of the water molecule is greater than the size of the N2 or 02. v) It acts as scattering centre for other frequencies which are lower than the frequency of blue light. 

vi) Blue colour scatters more than other colours.. 

vii) That is why sky appears blue.

5. Why does the sun appear reddish early in the morning?

A. It is due to scattering of light. Light near the horizons passes thicker layers of air and larg- er distance of atmosphere. Hence most of the blue light is scattered away and longer wave- length reach our eyes giving rise to reddish colour of sun.

A. Continuously changing atmosphere refract light from the stars by different amounts fro- m one moment to the other. When atmosphe- re refracts more starlight towards us the stars appears to be bright and when the atmo- sphere refracts less starlight then the stars appear to be dim. However the planets are nearer to us than the stars they appears to be comparatively bigger to us so they can not be considered as a point source, hence no twinkling is seen.

A. i) The ciliary muscle to which eye lens is att- ached helps the eye lens to change its focal length by changing radii of curvature of eye lens.

ii) When the eye is focussed on a distant object, the ciliary muscles are relaxed so that the focal length of eye lens has its maximum value which is equal to its dis- tance from the retina.

iii) When the eye is focussed on a closer object the ciliary muscles are strained and focal length of eye lens decreases. The ciliary muscles adjust the focal length in a such a way that the image is formed on retina.

iv) This process of adjusting focal length is called accommodation. 

v) Ciliary muscles are useful to see distant,closer objects clearly.

A. i) In a hot day due to rise in the temperature. Water vapour enters into atmosphere which leads to abundant presence of water molecules in atmosphere.

ii) These water molecules scatter the colours of other frequencies (other than blue). 

iii) All such colours of other frequencies reaches your eye and white colour is appeared.

A. Paper material is made up of fibre. It has some refractive index. The paper is stained with oil. If the refractive index of oil is simi- lar to that of paper, light passes from oil to paper. The light will not scatter and the paper become transparent.