What the spectrumspectrumspectrum of electromagnetic radiation looks like?
The properties of electromagnetic radiation, or electromagnetic waves, are described by several parameters. These include wave frequencyfrequencyfrequency, wavelength, periodperiodperiod and amplitudeamplitudeamplitude.
In the graphic description of the wave, the following concepts are also helpful: the peakpeakpeak, the troughtroughtrough, the rest position.
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Wavelength
Definition: Wavelength
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WavelengthwavelengthWavelength (symbol: λ, unit: m) is the distance between two points of maximum displacement of a wave, i.e. between successive peaks (or troughs). The longer the wave, the smaller its energy.
Amplitude
Definition: Amplitude
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AmplitudeamplitudeAmplitude (symbol: A, unit: m) is the maximum displacement of a given wave point from the rest position. The higher the amplitude, the higher the wave intensity.
Frequency
Definition: Frequency
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FrequencyfrequencyFrequency (symbol: f, unit: Hz) is the number of full displacements of a given wave point from the rest position made within 1 second.
Period
Definition: Period
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PeriodperiodPeriod (symbol: T, unit: s) is the time required for the given wave point to cover the distance equal to the wavelengthwavelengthwavelength.
Wave speed
Definition: Wave speed
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Wave speedwave speedWave speed (symbol: c - in a vacuum, v - in any medium, unit: ) - the speed with which a given wave point propagates in space. Electromagnetic waves in a vacuum move at the speed of light:
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Exercise 1
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The figure shows two electromagnetic waves.
1. Which wave has the greater intensity? 2. Which wave corresponds to higher‑energy radiation? 3. Which wave represents green light, and which represents infrared radiation?
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1. a 2. b 3. b - green light, a - infrared radiation
Exercise 2
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Compare the results of X‑ray measurements with radio waves:
1. Which one is moving at a higher speed? 2. Which one has a longer wavelength? 3. Which of them has a higher frequency?
1. Both types of radiation belong to electromagnetic waves, so they move at the same speed. 2. Radio waves are longer than X‑ray waves. 3. X‑rays have a higher frequency.
Exercise 3
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The global positioning system (GPS) that we use in mobile phones or navigation devices, e.g. in cars, requires very accurate timing and reading of the position of the satellites on the orbits. Each of the satellites uses an atomic clock that sends signals using two frequencies of 1575,42 MHz and 1227,6 MHz. Calculate the wavelengths that these frequencies correspond to. Specify what kind of waves they belong to.
19,029 cm and 24,421 cm, these are microwaves.
Task 1
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Popular laser pointers usually emit green, red and blue light. Search on the Internet for the wavelengths corresponding to the colour of light emitted by these pointers. Then calculate what frequencies they correspond to. Are pointers also available with different colours?
Compare how far the light beam of these pointers can reach.
What should you pay attention to when using them?
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Remember
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Electromagnetic waves are widely used in technology and medicine. We use them in everyday life using, for example, mobile phones, using satellite navigation, microwave ovens, doing examinations recommended by a doctor.
Exercises
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Exercise 4
Exercise 5
Find the information you need in the available sources and describe how the microwave oven works.
Exercise 6
Explain in English what parameters characterises the electromagnetic waves.