The electromagnetic spectrum

7.6 Describe the main features of the electromagnetic spectrum. 7.7 State that all electromagnetic waves travel with the same high velocity in a vacuum 7.8 Describe typical properties and uses of radiations in all the different regions of the electromagnetic spectrum including: radio and television communications (radio waves), satellite television and telephones (microwaves), electrical appliances, remote controllers for televisions and intruder alarms (infra-red), medicine and security (X-rays).

What is the electromagnetic spectrum? We are all familiar with LIGHT Light is part of the EM spectrum – it is an electromagnetic wave. There are several different types of EM waves. The EM spectrum is a way of classifying all the types of waves according to wavelength, frequency or energy.

What are Electromagnetic Waves? Electromagnetic waves are just like any other wave, with one exception: They are the only type of wave that can travel through a vacuum They are transverse waves They all travel at the same speed: 300,000,000 m/s (3x108 m/s)

Where do electromagnetic rays come from? All electromagnetic waves are produced from various forms of oscillating charges or currents. They are emitted when charged particles oscillate or lose energy in some way All of the waves are transverse waves which travel at the speed of light (3 X 108 ms-1)and involve oscillating electric and magnetic fields Waves in the EMS vary with respect to their wavelength, frequency and photon energy – waves with the highest frequency (smallest wavelength) will have the highest photon energy (and be potentially most dangerous)

Visible spectrum From the sun ultraviolet X ray Gamma rays Radio waves Type of emission Description Explanation Visible spectrum 4*1014 Hz to 8*1014 Hz From the sun ultraviolet 8*1014 to 3*1016 Hz; higher energy than visible light X ray 3*1016 to 3*1019 Hz ; next highest energy colliding high-energy electrons into a metal target, usually tungsten Gamma rays 3*1019 Hz  ; highest energy decay of excited nuclei of radioactive elements Type of emission Description Explanation Radio waves Very low energy level; 3*101 to 3*109 Hz from the alternating current of an LC circuit. Microwaves 3*109 to 3*1011 Hz Microwave ovens Infra-red 3*1011 to 4*1014 Hz; lower frequency than visible emitted from all objects at or near room temperature in the form of blackbody radiation.

7.8 Describe typical properties and uses of radiations in all the different regions of the electromagnetic spectrum including: radio and television communications (radio waves), satellite television and telephones (microwaves), electrical appliances, remote controllers for televisions and intruder alarms (infra-red), medicine and security (X-rays) Radio

Radio Waves Created by oscillations (vibrations) of electrons in a conductor. Very long wavelength (few km to few cm) – low frequency – so low energy waves. Used to transmit radio and TV signals. Travel in straight lines, but can be bounced off the upper atmosphere, so can travel around the world.

The Electromagnetic Spectrum Radio Micro- Waves

MICROWAVES formed from oscillating electrons within a magnetic field wavelength from cm to 0.1 mm used for cooking food microwaves make water molecules vibrate, which causes food to get very hot very quickly. penetrate only a few cm, the heat is then carried inside by conduction

MICROWAVES Microwaves are also used for communication. Mobile telephones use microwaves. They are also used to communicate with satellites as they can pass through the upper atmosphere They also do not spread out much, so they are easy to use with a dish.

The Electromagnetic Spectrum Infra Red Radio Micro- Waves

INFRA-RED Formed from heat, emitted by anything hot/warm. Wavelength from mm (1 x 10-3 m) to 1 x 10-6 m. Most familiar use is for cooking and heating, like electric grills and heaters. Infra red waves are easily absorbed at the surface of things, making them hot, then heat is carried inside by conduction.

INFRA-RED All matter emits infra-red rays – the hotter the matter, the more infra-red emitted This allows night-vision cameras to sense IR instead of visible light They are also used for thermal-imaging cameras, to find people buried in earthquakes. They are also used for remote controls

The Electromagnetic Spectrum Infra Red Radio Micro- Waves Visible

VISIBLE LIGHT Formed from very hot objects or the synchronisation of waves within a crystal (lasers) This is the EM wave we are most familiar with. Different colours have different wavelengths, from red (longest) to violet (shortest). Lasers emit a single wavelength (colour) of visible light

THE VISIBLE SPECTRUM The full spectrum is: ROYGBIV RED ORANGE YELLOW GREEN BLUE INDIGO VIOLET These can be remembered using: Richard Of York Gave Battle In Vain! ROYGBIV

The Electromagnetic Spectrum Infra Red Ultra Violet Radio Micro- Waves Visible

ULTRA VIOLET Formed from extremely hot objects (like the sun or sparks) OR exciting mercury vapour inside a fluorescent tube Shorter wavelength: 1 x 10-6 m to 1 x 10-9 m, frequency higher. Carry more energy, and can penetrate top layers of skin, damaging the lower layers This can cause sun burn, and possibly skin cancer of a long period of time. Your eyes are very sensitive to UV, so sunglasses should always be worn in bright sunshine. Most UV radiation from the sun is filtered by the ozone layer.

Ultra Violet UV rays can be used to sterilise things, as bacteria can be killed by UV. UV is also used for anti-counterfeit purposes in bank notes. Ultraviolet rays can cause some materials to fluoresce when they absorb them UV tubes are used in entertainment venues – they make white clothes glow

The Electromagnetic Spectrum Infra Red Ultra Violet Radio Micro- Waves Visible X-Rays

X-RAYS Discovered accidentally by Wilheim Röntgen in 1895 Formed from high speed electrons being fired at a metal target. Very short wavelength (1 x 10-8 to 1 x 10-12) and very high frequency. Very energetic – can pass through your body. Produced by firing electrons at a metal target

X-Rays Their ability to pass through soft tissue, but not bone, makes them very useful in medicine. They are completely stopped by metals, making them useful for security scanning at airports.

X-Rays and cancer/ cancer treatment Because they carry a lot of energy they can easily damage or kill cells. This can lead to cancer if over-exposure occurs. Very small amounts are used in hospitals and are relatively safe, however the operator will stand behind a lead screen to stop unnecessary exposure X-rays are also used to treat cancer by killing cancerous cells.

The Electromagnetic Spectrum Gamma Rays Infra Red Ultra Violet Radio Micro- Waves Visible X-Rays

GAMMA RAYS Extremely short wavelength (10-11 to 10 -14m) Extremely high frequency, so carry a large amount of energy. Gamma rays arise from the radioactive decay of nuclei of unstable atoms.

GAMMA RAYS and sterilisation Very harmful to living things – they can easily kill or damage cells leading to cancer. They are used to sterilise hospital equipment as bacteria are killed instantly on exposure They can also be used to kill bacteria in food. This is known as gamma irradiation.

GAMMA RAYS and cancer treatment A very important application of gamma rays is the treatment of cancer. More effective than X-rays because they carry more energy. Careful focussing of gamma rays avoids damage to healthy cells.