Electromagnetic Spectrum

In order of decreasing wavelength and increasing frequency:

Radio, Microwaves, Infrared, Visible light, Ultraviolet, Xrays, Gamma rays

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 They consist of an oscillating electric field with a oscillating magnetic field. They are at right angles to each other and to the direction of wave travel.

All of them are transverse and travel at the same speed in a vacuum (300,000,000 m/s)

They can transfer energy and can be reflected, refracted and diffracted. 

They obey: wave speed = wavelength x frequency

The wavelength varies from 10-15m to 103m. 

William  Herschel discovered infrared in 1800 when investigating the temperature of the visible spectrum. 

Infrared have longer wavelengths than red light. 

Causes skin burns.

They are used in cooking in the grill, toaster and oven.

Johann Ritter discovered ultraviolet in 1801, when experimenting with silver chloride in photography. 

Ultraviolet have a shorter wavelength than violet light. 

They are from the Sun and damage skin cells and eyes, It also results in sunburn and skin cancer. 

Ultraviolet lamps produce UV light when mercury vapour conducts electricty. It also sterilises water and kills bacteria. 

Radio waves are produced and detected by aerials. 

They broadcast TV and radio programmes, and used by the emergency services for communication. 

They are safe as don't produce ionisation.

Microwaves are very high frequency radio waves. 

They cook food, for they are absorbed by the water and fat in the food and the energy becomes heat. Also used for mobile phone communication. 

Causes internal heating of the body cells.

Medium frequency radio waves (MW) can reflect off the ionsphere to communicate long distances. The reflected waves are known as sky waves. 

High frequency radio waves travel in straight lines to satellites. 

Visible Light is the only part of the EM spectrum that can be seen by the naked eye.

Used in photography and for lighting homes and streets. Transmitted along optical fibres for communications. Glass fibres are lighter, cheaper and faster than copper fibres. 

Intense light can cause permenant damage to the retina. 

Radioactivity

Atoms consist of a nucleus surronded by electrons. Atoms that have unstable nuclei break down, releasing energy in the form of alpha, beta or gamma. This is radioactivity.

It occurs naturally and randomly. Not affected by temeprature or other conditions. 

All types of radiation transfer some energy to the atoms of the material they're passing through, causing electrons to get knocked off and making it a positive ion. This is known as ionisation.

Ionising radiation is detected using a Geiger Muller tube. When alpha or beta enter, it ionises the gas, producing a pulse of electrical charge, making the GM tube click. 

Xrays are produced when fast moving electrons hit a metal plate. 

Used to detect an object's internal structure, or used in airport security scanners, to detect unwanted pieces of metal in machinery and in medical x-rays to detect condition of bones.

In an Xray, a high voltage is applied between the electrodes. The electrons accelerate and hit a tungsten target. The electrons then collide with tungsten atoms and emit xrays. 

Gamma rays are produced by radioactive materials. 

They kill bacteria, sterilse food and medical instruments. 

Radioactive tracers emitting gamma are used to detect some cancers. Gamma is then used in radiotherapy to treat some cancers. 

Both can damage the DNA of cells, mutate cells and can trigger cancer.