The Electromagnetic Spectrum
Visão Geral
Hold your hand in front of a television remote control and press a button. Nothing happens. Point the remote at the television across a dark room and the channel changes instantly, with no wire, no sound and nothing at all for your eyes to see. Something crossed that room, carried energy from the little diode in the remote to the sensor on the television, and did it at three hundred million metres every second. It was the same kind of thing that lets you see this page, the same kind of thing that cooks a potato in a microwave oven, the same kind of thing that photographs the bone in a broken wrist. One family, one speed, one continuous spread of possibilities.
This lesson takes that family apart and puts it back in order. You will learn the sequence of the seven regions and what actually changes as you walk along it, why every object in the room around you is glowing in infrared right now and why a matt black surface glows harder than a shiny one, which regions carry our phone calls and our television and why each was chosen, and where along the sequence the radiation stops merely warming you and starts tearing electrons off your molecules. The last part of the lesson stays with X-rays: how a photograph of a bone is possible at all, why the same beam that finds a fracture can be aimed at a tumour, and what a radiographer wears so that a job spent beside an X-ray tube is a safe one.
Objetivos
- Electromagnetic waves are transverse waves that transfer energy from the source of the waves to an absorber.
- Electromagnetic waves form a continuous spectrum and all types of electromagnetic wave travel at the same speed through a vacuum (space). Students should know the order of electromagnetic waves within the spectrum, grouped in terms of energy, frequency and wavelength. They should appreciate that the wavelengths of the electromagnetic spectrum range from 10-15 m to 104 m and beyond.
- Visible light is the part of the electromagnetic spectrum that is detected by our eyes; we see different wavelengths as different colours.
- All objects emit and absorb infrared radiation. Objects emit infrared radiation because of the motion of their particles. The amount and frequency of emitted radiation depends on the temperature and surface of the object. The hotter an object is the more infrared radiation it radiates in a given time.; Dark, matt surfaces are good absorbers and good emitters of infrared radiation.; Light, shiny surfaces are poor absorbers and poor emitters of infrared radiation.; Light, shiny surfaces are good reflectors of infrared radiation.
- As an object heats up it radiates more and more infrared and radiation at higher frequencies.
- Black-body radiation is the range of electromagnetic radiation emitted by an object at a particular temperature.
- Radio waves, microwaves, infrared and visible light can be used for communication.
- Electromagnetic waves have many practical applications. For example: radio waves - television and radio systems (including Bluetooth); microwaves - mobile phones and satellite television systems; infrared - TV remote controls, night vision devices, heating; visible light - photography, fibre optic communications; ultraviolet - security marking; X-rays - medical imaging; gamma rays - sterilising surgical instruments and killing harmful bacteria in food.
- Excessive exposure of the human body to electromagnetic waves can be hazardous. Low energy waves have a heating effect and higher energy waves have enough energy to cause ionisation (remove an electron from an atom or molecule). For example: microwaves - heating of body tissue; infrared - skin burns; ultraviolet - skin cancer and blindness; X-rays - high doses kill cells; gamma rays - genetic mutations. Students should be able to describe simple protection measures against risks.
- X-rays are part of the electromagnetic spectrum. They have a very short wavelength, high energy and cause ionisation.
- Properties of X-rays include: they affect a photographic film in the same way as light; they are absorbed strongly by metal and bone; they are transmitted by healthy tissue.
- X-rays can be used to diagnose some medical conditions, for example in computed tomography (CT) scanning, bone fractures and dental problems. X-rays are also used to treat some conditions, for example in killing cancer cells.
- The use of high energy ionising radiation can be dangerous, and precautions need to be taken to monitor and minimise the levels of radiation that people who work with it are exposed to.
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- Which list gives four types of electromagnetic wave in order of increasing frequency? A. Infrared, microwaves, ultraviolet, X-rays B. Microwaves, infrared, ultraviolet, X-rays C. X-rays, ultraviolet, infrared, microwaves D. Ultraviolet, X-rays, microwaves, infrared Answer: B
- Two electromagnetic waves travel through a vacuum, one a radio wave and one a gamma ray. Which statement is correct? A. The gamma ray travels faster than the radio wave B. The radio wave travels faster than the gamma ray C. They travel at the same speed D. Neither can travel through a vacuum Answer: C
- Which type of electromagnetic radiation is used for security marking? A. Microwaves B. Infrared C. Ultraviolet D. Gamma rays Answer: C
- Four objects at the same temperature have different outer surfaces. Which surface emits infrared radiation at the greatest rate? A. Dark and matt B. Dark and shiny C. Light and matt D. Light and shiny Answer: A
- A microwave transmitter emits waves of frequency 6.0 x 10^9 Hz. Electromagnetic waves travel at 3.0 x 10^8 m/s. What is the wavelength of the waves? A. 0.005 m B. 0.05 m C. 0.5 m D. 20 m Answer: B
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Secção do manual
The Electromagnetic Spectrum
In this module we examine how electromagnetic waves are classified into categories such as radio, infrared, ultraviolet, and so on, so that we can understand some of their similarities as well as some of their differences. We will also find that there are many connections with previously discussed t
"College Physics: The Electromagnetic Spectrum" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/college-physics/pages/24-3-the-electromagnetic-spectrum. Access for free at https://openstax.org/books/college-physics/pages/1-introduction
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Secção do manual
Radiation
You can feel the heat transfer from a fire and from the Sun. Similarly, you can sometimes tell that the oven is hot without touching its door or looking inside—it may just warm you as you walk by. The space between the Earth and the Sun is largely empty, without any possibility of heat transfer by c
"College Physics: Radiation" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/college-physics/pages/14-7-radiation. Access for free at https://openstax.org/books/college-physics/pages/1-introduction
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