The human eye and the colourful world Worksheet-8

The human eye and the colourful world Worksheet-8

54. Calculate maximum power of accommodation of a person having normal vision.

55. Why cannot we read a printed page by holding it very close to our eyes ?

56. What are the important features of visual system of a person?

57. The fax point of a myopic eye is 80 cm in front of the eye. What is the power of the lens required to enable him to see far off objects ?

58. What kind of lens is used in the spectacles of a person suffering from myopia (near sightedness) ?

59. Write the function of Iris in the human eye.

60. Why does the sun appear reddish at sunrise ?

61. Why is red colour selected for danger signal lights ?

62. Why does sky look blue on a clear day ?

63. Explain about the colour of the sun at sunrise and sunset.

Answer:

54. For a person having normal vision, least distance of distinct vision is d = 25 cm.

∴ Maximum power of accommodation,

55. This is because focal length of eye lens cannot be decreased below a certain minimum limit 25 cm.

56. The structures of the eye such as cornea, pupil, ciliary muscles, eye lens, aqueous humour and vitreous humour etc.

The retina of eye which converts light signals to electrical impulses.

Optic nerve that transmits electrical impulses to brain.

57. Here,  x = 80 cm,  P = ?

As f = –x,   ∴ f  = –80 cm

Negative sign shows that the lens must be concave.

58. A concave lens.

59. Iris is a coloured muscular diaphragm. Its function is to regulate the amount of light entering the eye by adjusting the size of the pupil.

60. At sunrise, the light from the sun has to pass maximum distance through the earth's atmosphere. Red light being of largest wavelength is scattered the least. That is why the sun appears red.

61. Red colour has the largest wavelength. Therefore, it is scattered the least by fog or smoke. Hence it can be seen from maximum distance.

That is why red colour is selected for danger signal lights.

62. When sunlight passes through the atmosphere, it is scattered by molecules of air and other fine particles. As their size is smaller than the wavelength of light, therefore, blue colour which is of shorter wavelength is scattered more strongly than the red colour which is of larger wavelength. The scattered blue light enters our eyes and the clear sky looks blue.

63. At sunrise and sunset, the sun is near the horizon of earth. Light from the sun has to pass maximum distance through earth's atmosphere. So most of the blue light is scattered away. The light which reaches our eyes is of longer wavelength. That’s why the sun looks red at the time of sunrise and sunset.