The human eye and the colourful world Worksheet-7

The human eye and the colourful world Worksheet-7

 

  1. How do we see colours ?

 

  1. Why do different colours deviate through different angles on passing through a prism ?

 

  1. Give the meaning of the term VIBGYOR. With which phenomenon is it connected ?

 

  1. What is the condition for Raleigh scattering?

 

  1. What is the order of wavelength of visible light ?

 

  1. What is the size of an air molecule ?

 

  1. Can visible light be scattered by atoms/molecules in earth's atmosphere?

 

  1. Why does sky look blue ?

 

  1. What is the basic cause of atmospheric refraction ?

 

  1. What Is the nature of eye lens ? Is its focal length fixed ?

 

  1. A person has normal vision, but he cannot distinguish between red-green colours. Why ?

 

  1. What is meant by accommodation of human eye ? How is it achieved ?

 

  1. What is meant by range of vision ? What is its value for a person with normal vision ?

 

Answer:

  1. The retina of our eye contains numerous cells, which are light sensitive.

There are two types of cells : rod shaped and cone shaped

Rod Shaped cells respond to brightness/intensity of light and cone shaped cells respond to colour of light. When light falls on the retina, these cells get activated. They send electrical signals to the brain through the optic nerve. The brain processes this information and we see objects as they are. So we can say that colours are seen due to activation of cone shaped cells.

 

  1. Because different colours travel through glass with different speeds and glass has different refractive index for different colours.

 

  1. VIBGYOR represents the colour sequence in a visible spectrum. V stands for violet ; I for indigo ; B for blue ; G for green ; Y for yellow ; O for orange and R for red.

It is connected with the phenomenon of dispersion of white light.

 

  1. Size of scatterer must be much smaller than wavelength of incident light.

 

  1. 10–7 m.

 

  1. Around 1010 m.

 

  1. Yes, as size of molecule/atom is much less than wavelength of light.

 

  1. Because blue colour having smallest wavelength is scattered most, when visible light from the sun passes through earth's atmosphere.

 

  1. Variation in optical density of different layers of earth's atmosphere.

 

  1. Eye lens is a double convex lens. Its focal length is not fixed, but adjustable.

 

  1. He may be deficient in cone shaped cells having red and green pigment in the retina of his eyes. It is a genetic disorder and not a refractive defect of Vision. That is why the person has normal vision.

 

  1. The ability of the eye to observe distinctly the objects situated at widely different distances from the eye.

This property is due to the action of ciliary muscles holding the eye lens.

For observing distant objects, eye is in relaxed state. The eye lens is thin and image of distant object is formed on the retina. It is said to be unaccomodated.

For observing nearby objects, the ciliary muscles contract the eye is in a state of tension. It is said to be accommodated.

 

  1. It is the distance between near point (N) and far point (F) of his eyes.

The point at closest distance, at which an object can be seen clearly by the eye is called near point (N) of the eye.

The most distant point at which an object can be seen clearly is called far point (F) of the eye. For a normal eye, far point lies at infinity. Hence for a person with normal vision, the range of vision is infinite.