Exercises

  1. Fill in the blanks with the proper words:
  2. Click on the question to view the answer

400 nm to 800 nm

radio

Subramanian Chandrashekhar

Galileo

Nainital

  1. Form Pairs:
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Column A Column B
(i) X-rays (d) Chandra
(ii) Optical Telescope (c) Hubble
(iii) Indian Radio Telescope (a) GMRT
(iv) Launching artificial satellites (b) ISRO

  1. What are the difficulties in using ground based optical telescopes? How are they overcome?

  • The visible light coming from a heavenly body has to pass through the earth’s atmosphere to reach the earth’s surface.
  • During this journey, some of the light is absorbed by the atmosphere and the intensity of the light reaching the earth’s surface decreases.
  • A second problem is caused by the changes in atmospheric pressure and temperature.
  • These changes cause turbulence in the atmosphere which in turn cause of the light rays to change their path slightly and thereby shake the position of the image.
  • Also, because of Sunlight, we cannot use optical telescopes during the day. During the night too city lights and cloudy weather can cause difficulties in observing the heavenly bodies.
  • To reduce these problems, optical telescopes are situated on top of the mountains, at uninhabitated places.
  • However, if we want to get rid of all the above problems completely, we should place the telescope above the earth’s atmosphere, in the space itself.
  • These problems do not exist in the space and thus the image obtained by space telescopes would be sharp, bright, steady and very clear.


  1. Which type of telescopes can be made using a concave mirror, convex mirror, plane mirror and a lens? Draw diagrams of these telescopes.

Both Newtonian and Cassegrain types of optical telescopes can be made using these materials.

A line diagram of a Newtonian Reflector Telescope is shown here.

Newtonian Reflector Telescope

  1. Study the figure and answer the following questions:
Exercise 18 : Question 5

Newtonian Telescope

Exercise 18 : Question 5

Concave Mirror

Cassegrain Telescope

  • The distance between the concave mirror and the plane mirror can be adjusted.
  • The light rays coming from distant objects are parallel to each other.
  • These parallel rays are reflected from the concave surface of the mirror.
  • A diminished and inverted image is formed in front of the plane mirror.
  • This image is again reflected and serves as an object for the eyepiece.
  • The eyepiece acts like a simple microscope and a magnified image of the object is obtained.
  • Observer can see this image through the eyepiece.

  1. Answer the following questions:

  • Galileo’s telescope is a simple refracting telescope.
  • It consists of two convex lenses arranged coaxially in a metal tube.
  • Exercise 18 : Question 6 a
  • The distance between the lenses can be changed.
  • One of the lens is called the objective while the other is called the eye piece.

  • In addition to visible radiation, many heavenly objects emit radio waves. We cannot see this radiation with our eyes.
  • Hence, a special type of telescope is used to receive these rays. It is called a radio telescope.
  • Exercise 18 : Question 6 b
  • It is made from one or more dishes of a particular parabolic shape.
  • As in optical telescope the incident radio waves are reflected by these dishes and converge at the focus.
  • A radio receiver is placed at the focal point.

  • The waves and radiation emitted by the heavenly bodies passes through the atmosphere before reaching the earth.
  • Some part of this radiation is absorbed by the earth’s atmosphere and it’s intensity decreases.
  • In addition to this, temperature, cloud cover, air pressure etc. act as barriers to this radiation.
  • Bright sunlight during the day and city lights during the night also put limitations on using the optical telescopes.
  • To reduce the intensity of these problems, optical telescopes are placed in uninhabited places on mountains.

  • X-rays cannot reach the surface of the earth due to some constraints like atmosphere, temperature, air pressure, cloud cover.
  • Hence, X-ray telescope can not be based on earth.


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11 March 2022 at 23:36