# Long Physics Notes: Communications and Space: Not all dot points covered in this assignment

Essay by rarwdinosaurs July 2007

The World Communicates:

1.1 Recall two essential properties that distinguish electromagnetic waves from all other waves.

1) Electromagnetic waves do not require a medium to travel through - they can travel through a vacuum. They are caused by electric and magnetic fields oscillating together but perpendicular to each other so that the electromagnetic wave moves in a direction perpendicular to both of the fields [this is caused by accelerating charges, whereas other waves rely on vibrations].

2) All electromagnetic waves travel at the speed of light - 3.0 x 108 ms-1. Based on the formula v=fÃÂ, we can see that since v is a constant, then as the frequency increases, the wavelength decreases.

1.2 Identify bands of the electromagnetic spectrum that are significantly absorbed by the atmosphere.

Ã¢ÂÂSee figure 1.2.1 - Bands of the electromagnetic spectrum that are significantly blocked out by our atmosphere

The Earth's atmosphere absorbs most of the incoming EMR from space except for visible light and some high-frequency radio waves in the microwave region.

The other types of radiation would generally be harmful to us. Too much UV radiation would cause cancer and dangerous mutations. Too much penetration by X-rays or gamma rays would quickly kill us.

Higher frequency waves such as gamma, x-rays and some UV rays are blocked by the ozone and oxygen in the atmosphere.

Infra-red radiation is mostly blocked by carbon dioxide and water molecules in the atmosphere.

Low frequency radio waves are blocked by the electric charges in the upper atmosphere.

1.3 Explain why the data collected by astronomers is limited to a small section of the electromagnetic spectrum.

Many of the electromagnetic radiation bands are blocked by the earth's atmosphere. Astronomers can only detect the E.M.R that can penetrate the atmosphere. In particular, radio telescopes which detect the radio waves...