NCERT Class VIII Science Solutions: Chapter 16-Light Part 3

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Question 9:

Describe the construction of a kaleidoscope.

Answer:

A kaleidoscope is made up of three rectangular mirror strips joined together to form a prism. These are fix in a circular cardboard like tube or tube of a thick chart paper. The tube is slightly longer than the mirror strips. One end of the tube remains closed by a cardboard disc having a hole in the centre, through which one can see. To make the disc durable, a piece of transparent plastic sheet is pasted under the cardboard disc. At the other end, touching the mirrors, a circular plane glass plate is fixed. On this glass plate several small pieces of coloured glass is placed to form multiple images.

As showing in images is a construction of a kaleidoscope

Construction of a Kaleidoscope

Question 10:

Draw a labelled sketch of the human eye.

Answer:

As showing in images is a labelled sketch of the human eye

Labelled Sketch of the Human Eye

Question 11:

Gurmit wanted to perform Activity 16.8 using a laser torch. Her teacher advised her not to do so. Can you explain the basis of the teacher’s advice?

Answer:

Intensity of laser beam is very high, as it carries large amount of energy. It is harmful for eyes and can cause permanent damage. One should not look at laser beam directly or indirectly for a longer period.

Question 12:

Explain how you can take care of your eyes.

Answer:

It is necessary that we take proper care of our eyes. If there is any problem we should go to an eye specialist. Have a regular check-up.

  • If advised, we should use suitable spectacles.

  • Too little or too much light is bad for eyes. Insufficient light causes eyestrain and headaches. Too much light, like that of the sun, a powerful lamp or a laser torch can injure the retina.

  • We should not look at the sun or a powerful light directly.

  • Never rub our eyes. If particles of dust go into our eyes, wash our eyes with clean water. If there is no improvement go to a doctor.

  • Wash our eyes frequently with clean water.

  • Always read at the normal distance for vision. Do not read by bringing your book too close to our eyes or keeping it too far.

Question 13:

What is the angle of incidence of a ray if the reflected ray is at an angle of to the incident ray?

Answer:

We know that angle of incident ray is equal to angle of reflected ray.

⇒ ∠𝑖 = ∠𝑟

But it is given that