Electromagnetic spectrum

A prism can split white light into the familiar visible light spectrum, from red to violet. the spectrum shows all the wavelengths of visible light, arranged from the longest wavelength (red ) to the shortest (violet).

 Remember! Visible light is only a tiny part of the entire electromagnetic spectrum.  

The visible spectrum
The symbol for wavelength is the Greek letter lambda  (an upside down y)
the range of wavelengths of visible light is from 400nm (violet light) to 700nm (red light)
for exams make sure you remember a typical wavelength of visible light~ eg. (symbol for lambda )=500nm

Beyond the visible


Above is a diagram showing the electromagnetic spectrum. The electromagnetic spectrum includes wavelengths ranging over many orders of magnitude. it is divided into different regions, but the boundaries between them are not well defined .

For the exams you will need to learn:

• the names of the different regions in the electromagnetic spectrum
• the order they appear in 
• their approximate wavelength ranges

to make this easier i have created a table (below) so that all the information needed is included in the table. make sure you memorize this for the exams.

Region of spectrum	Range of wavelengths (shortest to longest)
Gamma Rays	10-16 to 10-10 m
X-rays	10-13 m to 10-8 m
Ultraviolet	10-8 m to 4x10-7 m (400nm)
Visible light	400nm to 700nm
Infrared	7x10-7 m (700nm) to 10-3 m
Microwaves	10-3 m to 10-1 m
Radio waves	10-1 m to 106 m or more

The Ultraviolet spectrum

The ultraviolet region of the electromagnetic spectrum is sub-divided into three parts:

UV-A - this is the longest wavelength (from 315nm to 400nm). this is the least hazardous form of UV Radiation. however over exposure can cause burning of the skin or even skin cancer. 

UV-B and UV-C have progressively shorter wavelengths, and are more hazardous. 

Sunscreen is used to block these rays so that they cannot penetrate the skin, causing cell damage and disrupting DNA. 

Speed of electromagnetic radiation

All types of electromagnetic radiation travel at the same speed through free space. this is often referred to as the speed of light, symbol C.

the SI system of units, the value of c is defined as C= 299 792 458 ms^-1

for calculations the approximate value of c is C=3x10^8ms^-1

Practical uses for electromagnetic radiation

Below is a table showing the practical uses for electromagnetic radiation , know some of these as you may be asked in exams to provide uses for the electromagnetic radiation.

Electromagnetic radiation	Uses
Gamma Rays	Medical: Destroying dangerous tissue: imaging with tracers. Industrial: sterilising items that may be contaminated with microorganisms; seeing inside solid objects (similar to x-rays).
X-rays	Medical: imaging inside the body. Industrial: seeing inside solid objects, e.g.  To detect cracks.
Ultraviolet	Medical: sterilisation; activating dental fillings. Industrial: sterilisation; visual security markings. Consumer: Reading DVD’s.
Visible light	People: sight. Consumer: reading CD’s.
Infrared	Consumer: remote controls, heating. Industrial: Transmission via optical fibres.
Microwaves	Consume: cooking. Industrial: telecommunications.
Radio waves	Medical: magnetic resonance imaging. Consumer: broadcasting, mobile phones. Industrial: Communicating with spacecraft; telecommunications.

Here is a video explaining how we use electromagnetic wave and how these waves interact.

Questions

1. The red limit of the visible spectrum is at about 700nm. Express this in standard form.
2. In what region of the electromagnetic spectrum does each of the following wavelengths lie?
   1 km, 800 nm, 500 nm, 1 nm
3. which section of the ultraviolet spectrum has the highest frequencies?
4. which of the following gives a good approximation to the speed of light in free space?
   300000 km s^-1, 300000000m s^-1, 300x10^6ms^-1
5. Roughly how many seconds does it take light to travel from the sun to the earth, a distance of 150 million km ?

By Ali Mannaraparambil