Electromagnetic spectrum • The electromagnetic spectrum is

more familiar to you than you might think. The microwave you use to heat your food and the cell phones you use are part of the Electromagnetic Spectrum. The light that our eyes can see is also part of the electromagnetic spectrum. This visible part of the electromagnetic spectrum consists of the colors that we see in a rainbow - from reds and oranges, through blues and purples.

• Each of these colors actually

corresponds to a different wavelength of light.

What are electromagnetic waves?

• Electromagnetic waves are formed when an electric field (shown as blue arrows) couples with a magnetic field (shown as red arrows). The magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave.

What speed do they move?

• Electromagnetic waves move at a speed of 299,792,458 metres per second (yes, you can round it up to 3 x 108 m/s. In other media, their speed is less

Electromagnetic Waves have different wavelengths

• Radio waves, television waves, and microwaves are all types of electromagnetic waves. They differ from each other in wavelength. Wavelength is the distance between one wave crest to the next.

• EM waves are typically described by any of the following two physical properties: the frequency f and wavelength λ,

The frequencies and wavelenghts of electromagnetic waves are related by the equation:

Energy of electromagnetic waves

All frequencies in the electromagnetic spectrum transmit energy at the speed of light. That’s why energy can be transferred by radiation (energy from the sun to the earth, the microwaves oven…)

How to calculate energy for electromagnetic waves

This energy is carried in smalll packs called photons. The energy per photon of an electromagnetic wave can be calculated from the Planck–Einstein equation:. hfE

where E is the energy, h is Planck's constant, and f is frequency

h = 6.626 × 10−34 joule-second

How do the waves fit into the electromagnetic spectrum?

Regions of the Electromagnetic Spectrum

Listed below are the approximate wavelength, frequency, and energy limits of the various regions of the electromagnetic spectrum.

Wavelength (m) Frequency (Hz) Energy (J)

Radio > 1 x 10-1 < 3 x 109 < 2 x 10-24

Microwave 1 x 10-3 - 1 x 10-1 3 x 109 - 3 x 1011 2 x 10-24- 2 x 10-22

Infrared 7 x 10-7 - 1 x 10-3 3 x 1011 - 4 x 1014 2 x 10-22 - 3 x 10-19

Optical 4 x 10-7 - 7 x 10-7 4 x 1014 - 7.5 x 1014 3 x 10-19 - 5 x 10-19

UV 1 x 10-8 - 4 x 10-7 7.5 x 1014 - 3 x 1016 5 x 10-19 - 2 x 10-17

X-ray 1 x 10-11 - 1 x 10-8 3 x 1016 - 3 x 1019 2 x 10-17 - 2 x 10-14

Gamma-ray < 1 x 10-11 > 3 x 1019 > 2 x 10-14

How do I remember all this?

 Try:RabbitsMateInVeryUnusualeXpensiveGardens

 meaning:RadioMicrowavesInfra-RedVisible lightUltra-violetX-raysGamma rays

Radio wavesThe wavelengths of radio waves are long compared to other types of electromagnetic waves—they range in length from 10,000 kilometers to less than a meter. Human-made radio waves are generated when electrons, which are negatively charged, move back and forth within an antenna. This movement of charged particles creates a field that radiates out from the antenna at the speed of light.

The radio portion of the electromagnetic spectrum is divided into bands. Some bands are dedicated to commercial, government, aviation, and maritime purposes.

Television stations use radio waves to broadcast their signals through the air, just as broadcast radio stations do. In fact, the TV band for channels 2-6 is next to the FM radio band

Microwaves

Microwave uses include finding planes in the sky and speeders on the ground (radar), sending a TV signal from a station to a broadcasting antenna (communication), and heating hot dogs (microwave ovens).

Can you feel the heat? (Well, imagine that you can.) You're in the infrared section of the electromagnetic spectrum. This part of the spectrum is also called radiant heat.

From people to planets, from incense candles to ice cubes, all objects give off infrared radiation. This radiation comes from the thermal motion of molecules. Naturally, the warmer an object is, the more infrared radiation it emits. An object that absorbs more infrared radiation than it releases becomes warmer.

INFRARED

Infrared radiation (2)

Infrared radiation is just below the red end of the visible spectrum. As the temperature of an object increases, it emits more IR radiation and of shorter wavelenghts, At 500ºC most pbjects start to emit visible red light as well.

Infrared is used in night vision equipment when there is insufficient visible light to see. It can be used to remotely determine the temperature of objects (if the emissivity is known). This is termed thermography. Infrared tracking, also known as infrared homing, refers to a passive missile guidance system which uses the emission from a target of electromagnetic radiation in the infrared part of the spectrum to track it.

Infrared radiation (3)

Infrared radiation can be used as a deliberate heating source. For example it is used in infrared saunas to heat the occupants, and also to remove ice from the wings of aircraft (de-icing).

IR data transmission is also employed in short-range communication among computer peripherals and personal digital assistants

Weather satellites equipped with scanning radiometers produce thermal or infrared images which can then enable a trained analyst to determine cloud heights and types, to calculate land and surface water temperatures, and to locate ocean surface features

The Visible Spectrum Richard Of York Gave Battle In Vain. = Red, Orange, Yellow, Green, Blue, Indigo, and Violet. are the colours of the visible spectrum. We cannot see Infra-red, but we can feel it warm our skin when we sit in the sun. Infra-red has a longer wavelength (less energy) than Red light. We cannot see Ultra-violet light, but we feel our skin has been burnt by the sun if we were in the sun too long yesterday. It is the Ultra-violet which is thought to cause skin cancer. UV light has a shorter wavelength (more energy) than visible light.

Ultraviolet radiation

• Extends from end of the visible light range to the X-ray region.

• Has a low power of penetration; hence, its direct effects on the human body are limited to the surface skin.

• It stimulates the production of vitamin D in the skin

Ultraviolet Radiation (2)• There are three categories of UV

radiation: – UV-A, between 320 and 400 nm – UV-B, between 280 and 320 nm – UV-C, between 200 and 280 nm

• Stratospheric Oxygen and Ozone molecules absorb 97-99% of the sun's high freguency Ultraviolet light

• Without the layer of ozone in the stratosphere to protect us from excessive amounts of UV-B radiation, life as we know it would not exist

Some questions…

• Which is the frequency of an infrared wave whose wavelength is 0.5 mm?

• Find the wavelength and frequency of a gamma ray photon that carries an energy equal to 10-12 Joules

• Which type of electromagnetic waves have an energy of 4 x 10-19 Joules?

X-rays • THEY CANNOT BE SEEN OR

FELT. X-RAYS MOSTLY PASS THROUGH SKIN AND SOFT TISSUE, BUT THEY DO NOT EASILY PASS THROUGH BONE OR METAL.

• X-RAYS ARE USED TO PRODUCE PHOTOGRAPHS OF BONES TO CHECK FOR DAMAGE SUCH AS FRACTURES. THEY ARE ALSO USED IN INDUSTRY TO CHECK METAL COMPONENTS AND WELDS FOR CRACKS OR OTHER DAMAGE.

• LOWER DOSES OF X-RAYS CAN CAUSE CELLS TO BECOME CANCEROUS

Gamma radiation

• These are the most energetic wavelengths of light, and they have the shortest wavelengths. Scientists know very little about what produces these wavelengths in outer space.

• They can pass through many kinds of materials, including human tissue. Very dense materials, such as lead, are commonly used as shielding to slow or stop gamma photons.

• They are used for:– cancer treatment – measure and control the flow of liquids in numerous industrial

processes– sterilize medical equipment in hospitals

– pasteurize certain foods and spices