Wednesday, September 10, 2008

What is Light ?

Light is a mixture of electrical and magnetic energy that travels faster than
anything else in the universe. It takes less than one lent of a second for light to
travel from New York to London. Light is made up of tiny particles of energy
called photons. The light moves along in very small waves that travel forward in straight lines, called rays. Light can travel through air and transparent substances, but can also travel through empty space. this is how sunlight reaches the earth. Light is similar to other forms of electromagnetic energy which have different wavelengths.


Radio Waves
These have the longest wavelength. They are used for satellite communication and to carry TV and radio signals.


Visible light
Appears white or colourless, but is made up of colours, each with a different wavelength.




Microwaves
Very short radio waves used in microwaves overs. They are also used in radar.




Electromagnetic spectrum
This show different kinds of electromagnetic energy arranged in order of their wavelength. Wavelength is the distance between two consecutive waves.






Infrared Rays
Invisible rays. but we can feel the heat from them. They can be used to detect cancer and arthritis, or to take photographs in the dark.




Ultraviolet Rays
These cause us to tan and help the skin to produce vitamin D. Large amounts are dangerous and may cause skin cancer, although most ultaviolet light from the sun is absorbed by the ozone layer.





X-Rays
Called "X" by their discoverer because he was unsure of their nature. they pass through flesh, but are absorbed by bones and teeth, causing them to show up on X-Ray film. Small doses are safe, but large amounts are harmful to living tissue.




Gamma Rays
These have the shortest wavelength. They are given off by naturally radioactive materials, such as uranium, and are part of the fallout after a nuclear explosion. They can travel through lead and cement, and damage living tissue.

1 comment:

jiwamusik said...

bring me back memories to my very old book "Lampu Belajar" by Sun Hok Gie (RIP)