P2 - Section B

Radiation

All types of radiation have a source that emits it. 

Radiation never stands still. 

Some radiation at the end of its journey, causes chemical change at the back of your eye. This radiation is known as visible light.

Materials like air, are good at transmitting light. These materials are either clear or transparent. 

One the way from the soure to you eyes light us more than likely going to be reflected by other materials. 

Objects around you would be invisble if they did not relect light. 

Radiation from the Sun contains infrared radiation, visible light and UV raditation.

Some of the radiation is transmitted through the atmosphere so it reaches the ground. 

Most of the harmful UV radiation is absorbed as the Sun's radiation passes downwards through the atmosphere. 

Life on Earth depends on the ozone layer absorbing UV radiation. 

O2 = Oxygen 

O3 = Ozone 

Troposphere = up to 15km 

Ozone layer = 15km to 30km 

Stratosphere = 15km to 50km 

The atmosphere is a mixture of gases, the main ones are: 

78% = Nitrogen

21% = Oxygen

1%   = Argon

When UV radiation is absorbed by the ozone layer, its energy can break ozone and oxygen molecules. This makes free atoms of oxygen. 

These chemical changes are reversible. Free atoms of oxygen in the ozone layer are always combining with oxygen molecules, which creates new ozone. 

Humans have created a problem, when it comes to ozone holes. Some synthetic (man-made) chemicals, such as CFCs (chlorofluorocarbons) used on fridges, have been escaping into the atmosphere. 

CFCs turn the ozone back into ordinary oxygen, which allows more UV radiation to reach the Earth's surface (through the hole in the ozone layer). This happens a lot over the north and south pole. 

To reduce the amount of CFCs in the atmosphere Aerosol cans no longer use CFCs and old fridges have the CFCs carefully removed at the end of their working life. 

Even with all this help, the ozone layer will take decades to get back to its original thickness.