Telescopes, Periscopes And Binoculars (T3)

Question 1

Describe optical telescopes…

Answer 1

• observe visible light from space
• small ones allow amateurs to view the night sky but there are very large optical telescopes around the world for professional astronomers to use
• some disadvantages are they can only be used at night and cannot be used in bad weather conditions

Question 2

Describe radio telescopes…

Answer 2

• detect radio waves coming from space
• although they are usually very large and expensive they have an advantage over optical telescopes in that they can be used in bad weather as radio waves are not blocked by clouds
• can also be used in daytime

Question 3

Describe X-ray telescopes…

Answer 3

• objects in the universe emit other electromagnetic radiation such as infrared, gamma and X-rays
• these are all blocked by the Earth’s atmosphere but can be detected be telescopes placed in orbit around the Earth

Question 4

Describe the prismatic periscope…

Answer 4

• light enters the top of the periscope and strike the surface of the prism at 45 degrees
• the critical angle for glass is 42 degrees so the light is totally internally reflected and is turned through 90 degrees
• light travels from the first prism to the second (bottom) which is again positioned so light is totally internally reflected
• the ray emerges parallel to the direction in which is was originally travelling
• the final image will be sharper and brighter than that produced by a periscope using two mirrors as no multiple images are created
• light entering the prism undergoes total internal reflection twice
• this system is used in bike reflectors and binoculars

Question 5

How do binoculars use the system of the prismatic periscope?

Answer 5

• each side of a pair of binoculars contains two prisms to reflect the incoming light
• without these, binoculars would have to be very long to obtain large magnifications