Presentation on the elctromagnetic spectrum prepared at Wilson´s Hospital School. Suitable for senior Physics.

6. 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…)

7. 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 : . where E is the energy, h is Planck's constant , and f is frequency h = 6.626 × 10 −34 joule-second

8. How do the waves fit into the electromagnetic spectrum?

10. Regions of the Electromagnetic Spectrum Listed below are the approximate wavelength, frequency, and energy limits of the various regions of the electromagnetic spectrum. > 2 x 10 -14 > 3 x 10 19 < 1 x 10 -11 Gamma-ray 2 x 10 -17 - 2 x 10 -14 3 x 10 16 - 3 x 10 19 1 x 10 -11 - 1 x 10 -8 X-ray 5 x 10 -19 - 2 x 10 -17 7.5 x 10 14 - 3 x 10 16 1 x 10 -8 - 4 x 10 -7 UV 3 x 10 -19 - 5 x 10 -19 4 x 10 14 - 7.5 x 10 14 4 x 10 -7 - 7 x 10 -7 Optical 2 x 10 -22 - 3 x 10 -19 3 x 10 11 - 4 x 10 14 7 x 10 -7 - 1 x 10 -3 Infrared 2 x 10 -24 - 2 x 10 -22 3 x 10 9 - 3 x 10 11 1 x 10 -3 - 1 x 10 -1 Microwave < 2 x 10 -24 < 3 x 10 9 > 1 x 10 -1 Radio Energy (J) Frequency (Hz) Wavelength (m)

11. How do I remember all this? meaning: R adio M icrowaves I nfra-Red V isible light U ltra-violet X -rays G amma rays Try: R abbits M ate I n V ery U nusual e X pensive G ardens

12. Radio waves The 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

13. 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).

14. 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

15. 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.

16. 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

17. The Visible Spectrum R ichard O f Y ork G ave B attle I n V ain. = 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.