P9 Electromagnetic spectrum IGCSE understand
- 1. 1 IGCSE Co-ordinated Science P9: Electromagnetic spectrum Acknowledgement: BBC Bitesize
- 3. 3 Syllabus - Core Describe the main features of the electromagnetic spectrum.
- 4. Electromagnetic radiation Electromagnetic radiation travels as waves and transfers energy from one place to another. All electromagnetic waves can travel through a vacuum, and they all travel at the same speed in a vacuum. 4
- 5. The electromagnetic spectrum The electromagnetic spectrum is a continuous range of wavelengths. The types of radiation that occur in different parts of the spectrum have different uses and dangers, which depend on their wavelength and frequency. 5
- 6. What is a spectrum? White light can be split up using a prism to form a spectrum. A prism is a block of glass with a triangular cross-section. The light waves are refracted as they enter and leave the prism. The shorter the wavelength of the light, the more it is refracted. As a result, red light is refracted the least and violet light is refracted the most, causing the coloured light to spread out to form a spectrum. 6
- 7. Types of electromagnetic radiation Visible light is just one type of electromagnetic radiation. There are various types of electromagnetic radiation, some with longer wavelengths than visible light and some with shorter wavelengths than visible light. You should know the different types of electromagnetic radiation and their typical uses. 7
- 8. Frequency Type of electromagnetic radiation Typical use Wavelength highest gamma radiation killing cancer cells shortest X-rays medical images of bones ultraviolet detecting forged bank notes by fluorescence visible light seeing infrared optical fibre communication microwaves cooking lowest radio waves television signals longest 8
- 9. 9 The electromagnetic spectrum Electromagnetic spectrum
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- 11. 11 Syllabus - Core Describe the role of electromagnetic waves in: • radio and television communications (radio waves), • satellite television and telephones (microwaves) • electrical appliances, remote controllers for televisions and intruder alarms (infrared) • medicine and security (X-rays).
- 12. Radiowaves: Television and radio Radio waves have lower frequencies and longer wavelengths than microwaves. They are used to transmit television and radio programmes. Television uses higher frequencies than radio. 12
- 13. Radiowaves: Television and radio A radio programme receiver does not need to be directly in view of the transmitter to receive programme signals. For low frequency radio waves diffraction can allow them to be received behind hills, although repeater stations are often used to improve the quality of the signals. 13
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- 16. Radiowaves: Television and radio The lowest frequency radio waves are also reflected from an electrically charged layer of the upper atmosphere, called the Ionosphere. This means that they can reach receivers that are not in the line of sight because of the curvature of the Earth's surface. 16
- 17. Radio waves reflected from the Ionosphere 17
- 18. Microwaves You should know some of the properties and uses of microwave radiation. Microwave radiation has lower frequencies and longer wavelengths than visible light. 18
- 19. Microwaves Microwave radiation is used for : Cooking Communication 19
- 20. Microwaves: Cooking Microwaves with certain wavelengths are absorbed by water molecules and can be used for cooking. Water in the food absorbs the microwave radiation, which causes the water to heat up and cook the food. The water in living cells can also absorb microwave radiation. As a result, they can be killed or damaged by the heat released. 20
- 21. Microwaves: Communication Microwave radiation can also be used to transmit signals such as mobile phone calls. Microwave transmitters and receivers on buildings and masts communicate with the mobile telephones in their range. Certain microwave radiation wavelengths pass through the Earth's atmosphere and can be used to transmit information to and from satellites in orbit. 21
- 22. Microwaves pass through the atmosphere 22
- 23. Microwaves: Communication One advantage is that the high frequency of microwaves gives the microwave band a very large information-carrying capacity; the microwave band has a bandwidth 30 times the radio spectrum below it. A disadvantage is that microwaves are limited to line of sight propagation; they cannot pass around hills or mountains as lower frequency radio waves can. 23
- 24. Microwave base station and repeaters Microwave base station Microwave repeaters 24
- 25. Infrared radiation You should know some of the properties and uses of infrared radiation. Infrared radiation has lower frequencies and longer wavelengths than visible light. 25
- 26. Uses of infrared Infrared radiation is used for cooking and heating. It is also used for communications signals, including TV remote controls and optical fibre communications. Information can be transmitted using analogue or digital signals. 26
- 27. Infrared sensors We cannot see infrared radiation, but we can feel it as heat energy. Infrared sensors can detect heat from the body. They are used in: security lights burglar alarms
- 28. Analogue and digital signals Communications signals can be analogue or digital. 28
- 29. Analogue signals Oscilloscope trace of an analogue signal. Music and speech vary continuously in frequency and amplitude. In the same way, analogue signals can vary in frequency, amplitude, or both. You may have heard of FM radio and AM radio - Frequency Modulated radio and Amplitude Modulated radio. The diagram above shows a typical oscilloscope trace of an analogue signal. 29
- 30. Digital signals Digital signals are a series of pulses consisting of just two states: ON (1) or OFF (0). There are no values in between. DAB radio is Digital Audio Broadcast radio - it is transmitted as digital signals. The diagram shows a typical oscilloscope trace of a digital signal. 30
- 31. Oscilloscope An oscilloscope is a laboratory instrument commonly used to display and analyze the waveform of electronic signals. In effect, the device draws a graph of the instantaneous signal voltage as a function of time. 31
- 32. Advantages of digital signals Digital signals carry more information per second than analogue signals. They are also less prone to interference and can carry more information. 32
- 33. Gamma radiation and X-rays You should know some of the properties and uses of gamma radiation and X-rays. Gamma waves have a very high frequency and very short wavelengths. 33
- 34. Gamma radiation and X-rays Gamma radiation cannot be seen or felt. This type of radiation mostly passes through skin and soft tissue, but some of it is absorbed by cells.
- 35. The Incredible Hulk http://www.youtube.com/watch?v=aoILzi5thYg http://www.youtube.com/watch?v=E7a5LcTckfg http://www.youtube.com/watch?v=kzVNa0gH3Y g
- 36. Gamma radiation Gamma radiation is used, among other things, for the following purposes: to sterilise surgical instruments to kill harmful bacteria in food to kill cancer cells (note that lower doses of gamma radiation could lead to normal cells becoming cancerous). 36
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- 38. X-rays X-rays have a lower frequency than gamma radiation. Like gamma 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 fractures. They are also used in industry to check metal components and welds for cracks or other damage. 38
- 39. Airport security In an airport scanner a conveyor belt carries each luggage item past an X-ray machine. Since different materials absorb X-rays at different levels, the image on the monitor lets the machine operator see distinct items inside your bag. Items are typically colored on the display monitor, based on the range of energy that passes through the object. 39
- 40. X-rays Lower doses of X-rays can cause cells to become cancerous, so precautions are taken in hospitals to limit the dose received by patients and staff when X-ray photographs are taken. 40
- 41. 41 Syllabus - Core Demonstrate understanding of safety issues regarding the use of microwaves and X-rays. Radioactivity – Topic 15
- 42. 42 Syllabus - Supplement State the approximate value of the speed of all electromagnetic waves in vacuo.
- 43. 43 The speed of electromagnetic waves The velocity at which light travels in vacuum is a physical constant: (approximately 3×108 meters/second). Light travels slower through any given material, or medium, that is not a vacuum.
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- 49. Task Now complete the end of chapter P15 questions on page 580 49
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- 55. 55 FINI