Прочитайте текст и определите какой из заголовков соответствует тексту Now let us turn to cathode-ra...: ответ на тест 781316 - Английский язык

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Now let us turn to cathode-ray tubes (abbreviated CRT) that provide a visual representation of voltage and current waveforms. Cathode-ray tubes consist of three basic components: 1. the electron gun, 2. a deflection system, 3. a fluorescent screen. These essential parts of a cathode-ray tube are mounted inside a highly evacuated, funnel-shaped glass envelope the large end of which has the fluorescent screen coated upon the inside surface.

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Now let us turn to cathode-ray tubes (abbreviated CRT) that provide a visual representation of voltage and current waveforms. Cathode-ray tubes consist of three basic components: 1. the electron gun, 2. a deflection system, 3. a fluorescent screen. These essential parts of a cathode-ray tube are mounted inside a highly evacuated, funnel-shaped glass envelope the large end of which has the fluorescent screen coated upon the inside surface.

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Among the most common meters used there are the ohmmeter, the ammeter and the voltmeter. The ohmmeter is used to measure the value of resistance. It consists of a milliammeter calibrated to read in ohms, a battery and resistors. The meter is connected in parallel and the circuit is not opened when its resistance is measured. The readings on the scale show the measured value.
The ammeter is used to measure the value of current. When the ammeter is used the circuit should be opened at one point and the terminals of the meter should be connected to it. One should take into consideration that the positive terminal of the meter is connected to the positive terminal of the source; the negative terminal - to the negative terminal of the source.
The ammeter should be connected in series. The readings on the scale show the measured value.

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A resistor is one of the most common elements of any circuit. Resistors are used:
1. to reduce the value of current in the circuit;
2. to produce IR voltage drop and in this way to change the value of the voltage.
When current is passing through a resistor its temperature rises high. The higher the value of current the higher is the temperature of a resistor. Each resistor has a maximum temperature to which it may be heated without a trouble. If the temperature rises higher the resistor gets open and opens the circuit.
Resistors are rated in watts. The watt is the rate at which electric energy is supplied when a current of one ampere is passing at a potential difference of one volt.

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An electric cell is used to produce and supply electric energy. It consists of an electrolyte and two electrodes. Electrodes are used as terminals, they connect the cell to the circuit - current passes through the terminals and the bulb lights.
Cells can be connected in series, in parallel and in series-parallel. In order to increase the current capacity cells should be connected in parallel. In order to increase the voltage output cells should be connected in series. In case a battery has a large current capacity and a large voltage output, its cells are connected in series-parallel.
When cells are connected in series the positive terminal of one cell is connected to the negative terminal of the second cell, the positive terminal of the second cell - to the negative terminal of the third ... and so on.
When cells are connected in parallel their negative terminals are connected together and their positive terminals are also connected.
In case a cell has a trouble it stops operating or operates badly. This cell should be substituted by another one.

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A capacitor is one of the main elements of a circuit. It is used to store electric energy. A capacitor stores electric energy provided that a voltage source is applied to it. The main parts of a capacitor are metal plates and insulators. The function of insulators is to isolate the metal plates and in this way to prevent a short.
There are two common types of capacitors in use nowadays: a fixed capacitor and a variable one. The plates of a fixed capacitor cannot be moved; for this reason its capacity does not change. The plates of a variable capacitor move; its capacity changes. The greater the distance between the plates, the less is the capacity of a capacitor. Variable capacitors are commonly used by radiomen; their function is to vary the frequency in the circuit. Fixed capacitors are used in telephone and radio work.