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Вопрос № 884769 - Английский язык

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A Radar System
1. A radar system has a transmitter that emits radio waves called radar signals in predetermined directions. When these come into contact with an object they are usually reflected and/or scattered in many directions. Radar signals are reflected especially well by materials of considerable electrical conductivity – especially by most metals, by seawater, by wet land, and by wetlands. The radar signals that are reflected back towards the transmitter are the desirable ones that make radar work. If the object is moving either closer or farther away, there is a slight change in the frequency of the radio waves, due to the Doppler effect.
2. Radar receivers are usually, but not always, in the same location as the transmitter. Although the reflected radar signals captured by the receiving antenna are usually very weak, these signals can be strengthened by the electronic amplifiers that all radar sets contain. The weak absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively-long ranges – ranges at which other electromagnetic wavelengths, such as visible light, infrared light, and ultraviolet light, are too strongly attenuated. In particular, there are weather conditions under which radar works well regardless of the weather. Such things as fog, clouds, rain, falling snow, and sleet that block visible light are usually transparent to radio waves.
3. Finally, radar relies on its own transmissions, rather than light from the Sun or the Moon, or from electromagnetic waves emitted by the objects themselves, such as infrared wavelengths (heat). This process of directing artificial radio waves towards objects is called illumination, regardless of the fact that radio waves are completely invisible to the human eye or cameras.
Ответьте на вопрос:
What enables radio waves to detect objects being far enough from radio transmitter?
Варианты ответов
  • It depends upon weather conditions.
  • It depends upon the property of the medium they go through.
  • It depends upon the frequency of electromagnetic waves.
  • It depends upon the intensity of radio waves’ reflection.
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Вопрос задал(а): Анонимный пользователь, 13 Ноябрь 2020 в 15:35
На вопрос ответил(а): Анастасия Степанова, 13 Ноябрь 2020 в 15:35

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Вопрос № 884764

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A Radar System
1. A radar system has a transmitter that emits radio waves called radar signals in predetermined directions. When these come into contact with an object they are usually reflected and/or scattered in many directions. Radar signals are reflected especially well by materials of considerable electrical conductivity – especially by most metals, by seawater, by wet land, and by wetlands. The radar signals that are reflected back towards the transmitter are the desirable ones that make radar work. If the object is moving either closer or farther away, there is a slight change in the frequency of the radio waves, due to the Doppler effect.
2. Radar receivers are usually, but not always, in the same location as the transmitter. Although the reflected radar signals captured by the receiving antenna are usually very weak, these signals can be strengthened by the electronic amplifiers that all radar sets contain. The weak absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively-long ranges – ranges at which other electromagnetic wavelengths, such as visible light, infrared light, and ultraviolet light, are too strongly attenuated. In particular, there are weather conditions under which radar works well regardless of the weather. Such things as fog, clouds, rain, falling snow, and sleet that block visible light are usually transparent to radio waves.
3. Finally, radar relies on its own transmissions, rather than light from the Sun or the Moon, or from electromagnetic waves emitted by the objects themselves, such as infrared wavelengths (heat). This process of directing artificial radio waves towards objects is called illumination, regardless of the fact that radio waves are completely invisible to the human eye or cameras.
Завершите утверждение согласно содержанию текста.
Unlike visible light radio waves …
can reflect from moving objects
are not detectible by human eyes
can be reflected from any object
are not usually influenced by weather conditions

Вопрос № 884774

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A Radar System
1. A radar system has a transmitter that emits radio waves called radar signals in predetermined directions. When these come into contact with an object they are usually reflected and/or scattered in many directions. Radar signals are reflected especially well by materials of considerable electrical conductivity – especially by most metals, by seawater, by wet land, and by wetlands. The radar signals that are reflected back towards the transmitter are the desirable ones that make radar work. If the object is moving either closer or farther away, there is a slight change in the frequency of the radio waves, due to the Doppler effect.
2. Radar receivers are usually, but not always, in the same location as the transmitter. Although the reflected radar signals captured by the receiving antenna are usually very weak, these signals can be strengthened by the electronic amplifiers that all radar sets contain. The weak absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively-long ranges – ranges at which other electromagnetic wavelengths, such as visible light, infrared light, and ultraviolet light, are too strongly attenuated. In particular, there are weather conditions under which radar works well regardless of the weather. Such things as fog, clouds, rain, falling snow, and sleet that block visible light are usually transparent to radio waves.
3. Finally, radar relies on its own transmissions, rather than light from the Sun or the Moon, or from electromagnetic waves emitted by the objects themselves, such as infrared wavelengths (heat). This process of directing artificial radio waves towards objects is called illumination, regardless of the fact that radio waves are completely invisible to the human eye or cameras.
Определите основную идею текста.
People use radar systems which are provided with a transmitter emitting radio waves which are reflected and/or scattered in many directions when coming into contact with an object.
Radar relies on its own transmissions, rather than light from the Sun or the Moon, or from electromagnetic waves emitted by the objects themselves.
Unlike visible light radio waves don’t depend much on the medium they go through while detecting objects at relatively-long distances.
Radar systems possess important properties enabling people to detect moving or still objects being far away from radio transmitter regardless of weather conditions.

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Вопрос № 884770

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Radio Systems
1. Radio systems used for communications will have the following elements. With more than 100 years of development, each process is implemented by a wide range of methods, specialized for different communications purposes. Each system contains a transmitter. This consists of a source of electrical energy, producing alternating current of a desired frequency of oscillation. The transmitter contains a system to modulate some property of the energy produced to impress a signal on it.
2. This modulation might be as simple as turning the energy on and off, or altering more subtle properties such as amplitude, frequency, phase, or combinations of these properties. The transmitter sends the modulated electrical energy to a tuned resonant antenna; this structure converts the rapidly changing alternating current into an electromagnetic wave that can move through free space.
3. The electromagnetic wave is intercepted by a tuned receiving antenna; this structure captures some of the energy of the wave and returns it to the form of oscillating electrical currents. At the receiver, these currents are demodulated, which is conversion to a usable signal form by a detector sub-system. The receiver is «tuned» to respond preferentially to the desired signals, and reject undesired signals.
Ответьте на вопрос:
Why does a modulation system serve for in a transmitter?
This system is used for oscillating electrical currents.
This system produces current of a desired frequency of oscillation.
This system can demodulate electric currents.
This system changes some quality of electrical energy.

Вопрос № 884771

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A Satellite Telephone
1. A satellite telephone, satellite phone, or satphone is a type of mobile phone that connects to orbiting satellites instead of terrestrial cell sites. They provide similar functionality to terrestrial mobile telephones: voice, short messaging service and low-bandwidth Internet access are supported through most systems. Depending on the architecture of a particular system, coverage may include the entire Earth, or only specific regions. The mobile equipment, also known as a terminal, varies widely.
2. Early satellite phone handsets had a size and weight comparable to that of a late-1980s or early-1990s mobile phone, but usually with a large retractable antenna. More recent satellite phones are similar in size to a regular mobile phone while some prototype satellite phones have no distinguishable difference from an ordinary smartphone. Satphones are popular on expeditions into remote areas where terrestrial cellular service is unavailable.
3. Since satellite phones are purpose-built for one particular network and cannot be switched to other networks, the price of handsets varies with network performance. If a satellite phone provider encounters trouble with its network, handset prices will fall, then increase once new satellites are launched. Similarly, handset prices will increase when calling rates are reduced.
Ответьте на вопрос:
What can be considered to be an imperfection of satellite telephony?
Early satphones are comparable in a size and weight to that of late-1980s or early-1990s mobile phones.
Satellite phones provide similar functionality to terrestrial mobile telephones.
One has to make fewer calls in order satellite phones to be cheaper.
The price of satellite phones depends on their network provider performance being invariable for them.

Вопрос № 884772

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Applications of radar
1. The information provided by radar includes the bearing and range (and therefore position) of the object from the radar scanner. It is thus used in many different fields where the need for such positioning is crucial. The first use of radar was for military purposes: to locate air, ground and sea targets. This evolved in the civilian field into applications for aircraft, ships and roads.
2. In aviation, aircraft are equipped with radar devices that can warn of obstacles in or approaching their path and give accurate altitude readings. They can land in fog at airports equipped with radar-assisted ground-controlled approach (GCA) systems, in which the plane's flight is observed on radar screens while operators radio landing directions to the pilot.
3. Marine radars are used to measure the bearing and distance of ships to prevent collision with other ships, to navigate and to fix their position at sea when within range of shore or other fixed references such as islands, buoys, and lightships. In port or in harbour, vessel traffic service radar systems are used to monitor and regulate ship movements in busy waters.
4. Radar has invaded many other fields. Meteorologists use radar to monitor precipitation. It has become the primary tool for short-term weather forecasting and to watch for severe weather such as thunderstorms, tornadoes, winter storms, precipitation types, etc.
Определите основную идею текста.
Radar device facilitates people’s life and work in different civilian fields.
Nowadays people can’t imagine their life without radar devices.
Radar devices are widely used by militaries in aviation and shipping.
Radar is a device providing people’s safety due to its distinctive characteristics.

Вопрос № 884773

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Radio waves
1. Radio waves were first predicted by mathematical work done in 1865 by James Clerk Maxwell. Maxwell noticed wavelike properties of light and similarities in electrical and magnetic observations. He then proposed equations that described light waves and radio waves as waves of electromagnetism that travel in space. In 1887, Heinrich Hertz demonstrated the reality of Maxwell's electromagnetic waves by experimentally generating radio waves in his laboratory. Many inventions followed, making practical the use of radio waves to transfer information through space.
2. The study of electromagnetic phenomena such as reflection, refraction, polarization, diffraction and absorption is of critical importance in the study of how radio waves move in free space and over the surface of the Earth. Different frequencies experience different combinations of these phenomena in the Earth's atmosphere, making certain radio bands more useful for specific purposes than others.
3. In order to receive radio signals, for instance from AM/FM radio stations, a radio antenna must be used. However, since the antenna will pick up thousands of radio signals at a time, a radio tuner is necessary to tune in to a particular frequency (or frequency range). This is typically done via a resonator (in its simplest form, a circuit with a capacitor and an inductor). The resonator is configured to resonate at a particular frequency (or frequency band), thus amplifying sine waves at that radio frequency, while ignoring other sine waves. Usually, either the inductor or the capacitor of the resonator is adjustable, allowing the user to change the frequency at which it resonates.
Определите основную идею текста.
Electromagnetic waves have a lot of important properties, being sent through space is one of the most significant of them.
The study of electromagnetic phenomena is of critical importance in the study of how radio waves move in free space and over the surface of the Earth.
It’s hard to imagine today’s life without the application of the devices based on the functioning of electromagnetic waves.
The discovery of electromagnetic waves enabled people to transfer information in space and caused many other important inventions improving humans’ life.
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