Test on the section of Electrical Engineering. Technology. 8th grade. Task #1 Basic sources of electrical energy

Никита_7203

8

Task #1 Basic sources of electrical energy:

1) Lighting devices: Lighting devices, such as light bulbs or fluorescent lamps, are one of the basic sources of electrical energy. When an electric current flows through them, they produce light energy, which is a form of electrical energy conversion.

2) Rectifiers: Rectifiers are another source of electrical energy. They are electronic devices that convert alternating current (AC) into direct current (DC). This conversion allows for the efficient use of electrical energy in various electronic devices and systems.

3) Heating devices: Heating devices, like electric heaters or stoves, also serve as basic sources of electrical energy. They convert electrical energy into heat energy, which can be used for heating homes, cooking food, or other purposes.

4) Thermal, atomic, and hydroelectric power stations: These power stations are large-scale sources of electrical energy. Thermal power stations generate electricity by burning fossil fuels, such as coal or natural gas, to produce steam, which then drives turbines connected to generators. Atomic power stations use nuclear reactions to produce heat, which is then converted into electricity. Hydroelectric power stations generate electricity by harnessing the energy of flowing or falling water, typically in dams or rivers.

Task #2 Transformers allow:

1) To convert alternating current into direct current: Transformers are not used for converting AC into DC. Rectifiers are the devices utilized for this purpose.

2) To convert direct current into alternating current: Transformers are not used for converting DC into AC. Electronic devices called inverters or converters are used for this purpose.

3) To convert alternating current of one voltage and frequency into alternating current of another voltage and the same frequency: This is the correct statement. Transformers are used to change the voltage level of an AC power supply while keeping the frequency unchanged. They consist of two or more coils of wire called windings. By adjusting the number of turns in each winding, the ratio of input to output voltage can be determined.

4) To change the frequency of current oscillations at the input: Transformers cannot change the frequency of current oscillations. Devices like frequency converters or electronic circuits are used for altering the frequency of an AC power supply.

Task #3 The thermal action of electric current:

The thermal action of electric current refers to the phenomenon of electrical energy being converted into heat energy when an electric current passes through a conductor. This effect is utilized in various electrical devices, such as electric heaters, kettles, toasters, and stovetops.

According to Joule"s law, the amount of heat produced in a conductor is directly proportional to the square of the current passing through it, the resistance of the conductor, and the duration of the current flow. This can be mathematically represented as:

\[Q = I^2 \cdot R \cdot t\]

Where:
- Q is the heat generated in joules (J),
- I is the current in amperes (A),
- R is the resistance of the conductor in ohms (Ω),
- t is the time in seconds (s).

The thermal action of electric current is also responsible for the operation of various household appliances that rely on heating elements, such as electric irons, hair dryers, and ovens. It is important to handle electrical devices with caution to prevent any potential hazards associated with the generation of excessive heat.