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# Electromagnetic waves

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### Electromagnetic waves

1. 1. Electromagnetic Spectrum
2. 2. Instructions• Duration of Lesson: 60 Min• Read through this powerpoint presentation and attempt the EM wave quiz• You can also find this chapter in your textbook, chapter : The grades of the quiz will be taken into you CA for semester 2, and you can only do it ONCE, so please make sure you understand the content of this unit.
3. 3. IntroductionObjectives:At the end of the lesson, you will be able to• Describe the main components of the electromagnetic spectrum.• State the properties of ALL EM waves.• Discuss the role of the respective EM waves and some of their applications.
4. 4. What are Electromagnetic Waves ?• If you have ever tuned in to listen to a radio, spoken on a handphone, turned on a light, had an X-ray taken, felt the warmth of sun on your skin.• You have experienced electromagnetic wave
5. 5. Electromagnetic wave Electric fieldProduced by Simultaneous vibration Magnetic field Electric field Magnetic field http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=52
6. 6. Wavelength of Electromagnetic Waves
7. 7. Hence this is the complete EM wave spectrum (the waves below in  ascending order of wavelength; descending order of frequency ) Gamma x-rays Ultra-violet Visible Infra- Microwave Radio wave rays ray light red rayHighest f Lowest fShortest λ Longest λ
8. 8. Properties of EM Wave1. All electromagnetic waves are transverse wave
9. 9. 2. They do not require any medium to travel through (recall: Radiation Infra red is an EM Wave)3. They travel at the speed of 3x108 ms-1 in vacuum (recall: speed of light  light is also an EM Wave)
10. 10. 4. They can all be reflected or refracted
11. 11. 5. They can all be emitted or absorbed by matter
12. 12. 6. They all obey the wave equation v =f x λWhere v = speed of wave (m/s) f = frequency of wave (Hz) λ = wavelength (m)
13. 13. 7. Their frequencies do not change as they pass from one medium to another. However, both their speed and wavelength will change. v =f x λ
14. 14. 8. They carry energy frm one place to another9. They are all of neutral charge as all of them oscillate with electric and magnetic field perpendicular to each other.
15. 15. Overview of EM waves Waves Longitudinal Waves Transverse Waves Sound waves Electromagnetic Waves Classified into Properties Comprises of Electromagnetic Spectrum Radiowave Infra-Red Ultra-Violet Gamma ray Microwave Light X-ray Applications
16. 16. Gamma raysGamma rays have the shortestwavelengths and highestfrequencies in the EM spectrum.It is generated by :Changes in energy levels in the nucleusSome radioactive substances and certainnuclear reactions produce gamma rays.Because of their great penetrating ability,gamma rays can cause serious illness.However when used in controlledconditions, gamma rays is useful in cancertreatment.
17. 17. X-raysX
18. 18. Both Gamma rays and X- rays can bedetected by:a) photographic platesb) ionization chamberc) phosphorescence
19. 19. Ultra-violetThe main source of ultra-violet radiation is sunlight and it is this radiation which gives rise to suntan and also sunburn.Ultra-violet radiation is used in hospitals to sterilize the surgical instruments and operating theatres as it kills bacteria and viruses.UV can be detected by:a) Photographic platesb) Photoelectric cellc) Fluorescence
20. 20. Visible LightVisible light is the part of the EMspectrum which can be detected by thehuman eye.The visible light has its own spectrumwhich consist of the 7 colours of light :Red Orange Yellow Green Blue IndigoVioletAn example of visible light is thecolourful laser light or the light from afirework.Some of the uses of light is inoptical fibres in medicine andtelecommunications.
21. 21. Infra-red wavesHeat can be transferred through infraredradiation.We often think of infra red as being the samething as heat, because it makes our skin feelwarm.Most of you might have seen infra-red waves in useduring the SARS period. (picture on the top right handcorner). It shows a thermo-detector which is placedoutside hospitals/airport to identify the warm and coolparts of a person by analyzing infra-red radiationemitted from the person’s body. And through this wecan see if someone is having a fever.Infra red is useful for:- For navigation through fog & haze as it is lesseasily scattered compared to visible light- Medical treatment : to warm injured muscles/sportsinjuries
22. 22. Microwaves One of their most common uses is in microwave ovens. When you switch on a microwave oven , it gives off electromagnetic waves that bounce around inside the oven, penetrating the food. Water molecules in the food absorb the energy from the microwaves, causing the food to get hot.Other uses of microwaves:a) Radar communication (as it is not easily blocked of by buildings/trees)b) Analysis of fine details of molecular and atomic structurec) Useful demonstration of all wave properties on macroscopic scaled) Telephone communication (mobile phones, etc)