(a) Give reason for the following:
- Colour of the clear sky is blue.
- We cannot see an object clearly if it is placed very close to the eye.
(b) What is Presbyopia? Write two causes of this defect.
(a)
1.Sky appears blue because blue colour has shorter wavelength than red. So, due to
different kinds of particulate matter such as smoke, dust, water particles, blue colour of light is scattered most. Hence, the sky appears to us as blue.
2.If an object is placed at a distance even less than 25 cm then the eye lens can not form its image at the retina. Thus, one cannot see that object.
(b) Presbyopia: With growing age, a person is unable to read and write comfortably. This called presbyopia. It causes due to :
- Weakening of ciliary muscles.
- The eye lens loses it’s some flexibility or elasticity.