Light Worksheet-9

Light Worksheet-9

 

  1. What is colour blindness? Give reason for this defect?

 

  1. What is a nictating membrane? In which animal is it found?

 

  1. What kind of eyes do the insects have?

 

  1. What is short sightedness? How is it corrected?

 

  1. What is long sightedness? How is it corrected?

 

  1. What kind of problem develops when the lens becomes thick?

 

  1. What kind of problem develops when the eye lens becomes flat?

 

  1. Why should children take milk and eat carrots?

 

  1. How is night blindness caused?

 

  1. Is the moon a luminous body? How are we able to see the moon?

 

  1. Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30° as shown in the figure. Draw the reflected ray from the second mirror.

 

  1. How are we able to see objects?

 

  1. What are cones and rods? What are their functions?

 

  1. (a) In a periscope two mirrors are arranged parallel to each other but they do not form multiple images. Why?

(b) What is the use of periscope?

 

  1. Draw a diagram to show dispersion of light.

 

Answer:

  1. Some people cannot distinguish between the different colours. This is known as colour blindness. Colour blindness is due to the absence of cones on the nerve endings on the retina.

 

  1. Nictating membrane is a transparent membrane over the eye to protect the eye from water. Fish and Frogs have a nictating membrane.

 

  1. Insects have compound eyes with hundreds of small units, each with a lens of its own. The image seen by a insect is a blurred picture.

 

  1. A person with short sight can see nearly objects but not far away objects. It can be corrected by using a concave lens.

 

  1. A person with long sight can see far away objects clearly but cannot see nearby object clearly. It can be corrected by using a convex lens.

 

  1. When the eye lens becomes thick, the person cannot see the distant objects clearly.

 

  1. When the eye lens becomes flat the person cannot see nearby things clearly.

 

  1. Milk, carrots and yellow fruits are rich in vitamin A, which is very essential for the eyes to maintain good vision and health.

 

  1. Night blindness is caused by the deficiency of vitamin A and damage to the retina and the rods.

 

  1. The moon is non-luminous. We are able to see the moon because it reflects the sunlight falling on it.

 

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  1. The lens focuses the light on the back of the eye on the retina. Retina contains several nerve cells which transmit the sensations to brain through the optic nerve. We are then able to see the objects.

 

  1. Cones are the nerve endings which are sensitive to colour light. They help us to distinguish between colours.

Rods are the nerve endings which are sensitive to bright light.

 

  1. (a) In a periscope two mirrors are placed parallel and facing each other but are in an inclined position at an angle of 45°. So they do not form multiple images.

(b) Uses of periscope – in submarines to view the happening on the surface of water.

                             – to view objects behind the wall.

 

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