recognize different types of electromagnetic waves.
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Before you start, answer the question.
How the information is sent using mobile phones?
Electromagnetic waves
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Electromagnetic waves are an effect of an oscillationoscillationoscillation of electric and magnetic fields. They are also called electromagnetic radiationradiationradiation, light or photons.
Electromagnetic radiationradiationradiation propagates in the vacuum at a constant speed of about 3 ∙ 10Indeks górny 88. It propagates in the wave motion. The electric field oscillates in a perpendicular plane to the magnetic field oscillationoscillationoscillation plane. Both oscillation planes are perpendicular to the direction of the wave motion.
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Frequency and wavelength
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The propagationpropagationpropagation of electromagnetic waves can be described in any medium by the relation:
where: λ - is the wavelength, v - its speed, f - the frequencyfrequencyfrequency.
In the vacuum electromagnetic waves travel with the speed of light and this formula can be rewritten as:
where: c - is the speed of light.
The electromagnetic wave transfers energy not in a continuous manner but in portions, called quanta. The smaller the wavelength, the larger the portions of energy carried by the wave.
Calculate the parameters of an electromagnetic wave.
Exercise 1
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An electromagnetic waveelectromagnetic waveelectromagnetic wave travels in vacuum and has a length of 7,5 ∙ 10Indeks górny -2-2 m. What is its frequencyfrequencyfrequency?
f = 4 ∙ 10Indeks górny 99 Hz
Types of electromagnetic waves
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Electromagnetic waves play very important role in our daily life. We use them in communication technology, in science and industry, in medicine, in culture and entertainment.
Electromagnetic waveselectromagnetic waveElectromagnetic waves are used to transmit radio signals (long, short and ultrashort waves) as well as TV signals, mobile phone and wireless devices signals. They are also used for transmitting energy in the form of microwaves, infrared radiationradiationradiation (IR), visible light (VIS), ultraviolet light (UV), X‑rays, and gamma rays.
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γ‑rays
Definition: γ‑rays
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Gamma rays have the smallest wavelengths and carry the largest portion of energy among the waves in the electromagnetic spectrumelectromagnetic spectrumelectromagnetic spectrum. They are produced by stars and by some radioactive substances.
X‑rays
Definition: X‑rays
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X‑rays carry also a large portions of energy and have high frequencies. They are used for medical imaging, treating cancer and even used for exploring the cosmos.
Ultraviolet rays
Definition: Ultraviolet rays
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Ultraviolet rays are invisible to humans, but visible to a number of insects and birds.
Ultraviolet rays make black‑light posters glow and are responsible for summer tans — and sunburns.
Visible spectrum
Definition: Visible spectrum
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Human eyes are sensitive to only a very narrow band of electromagnetic waves referred as the visible light spectrum. In daily life this spectrum is called simply “light”. The range of the visible light is from approximately 700 nanometers (abbreviated nm) to approximately 400 nm. Expressed in SI units, the range of wavelengths extends from 7 ∙ 10Indeks górny -7-7 m to 4 ∙ 10Indeks górny -7-7 m.
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The sense of sight is the most sensitive to green and its shades. Therefore, green lights are used as a signal to move in traffic. It is also worth to use this color when we are recording important information. Among the many lines of monochrome (black, blue) text, the eye will focus on the part written (marked) in green.
Infrared radiation
Definition: Infrared radiation
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Infrared radiationradiationradiation is used in industrial, scientific, and medical applications. They are also used in night‑vision cameras.
Microwaves
Definition: Microwaves
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Microwaves are most often used in satellite communications, when transmitting radar, telephone and navigation signals.
Radio waves
Definition: Radio waves
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Radio waves are used to transmit radio signals emitted by e.g. radio broadcasting stations, radar devices, and other navigation systems, communication satellites.
Exercise 2
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Why an application of a UV cream is recommended in very sunny days?
It protects the human skin from getting too much UV radiationradiationradiation, and also decreases the danger of getting the skin cancer.
Remember
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Electromagnetic waves are created as a result of oscillationoscillationoscillation of an electric field and a magnetic field.
Electromagnetic waves play very important role in our daily life. We use them in communication technology, in science, industry and medicine.
Exercises
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Exercise 3
Exercise 4
Arrange the listed electromagnetic waves according to the increasing wavelength: X‑rays, visible light spectrum, infrared waves, radio waves, microwaves, gamma rays.