XIV. Form one sentence of each pair of sentences using the Absolute Participle Construction.

Model: The train had left; we went home.

The train having left, we went home.

1. Atoms split in the reactor; heat is developed.

2. There are many different sources of energy; coal is the most important of them.

3. Atomic energy replaces the present sources of energy; we shall get more energy in the future.

4. The reactor produces energy in the form of heat; heat is developed lowing to the splitting of atoms in the reactor.

5. A nuclear power station is like any other power station; the coal-burning furnace is replaced by a nuclear reactor.

XV. Read text 3 b. Find the answers in text 3 b to the following questions:

1. What is the task of a transformer?

2. What practical purposes can it serve for?

3. What major parts does a transformer include?

4. What example demonstrates that transformers reverse voltage through electromagnetic induction?

5. What kinds of transformers are known to you?

6. What is each of them characterized by?

Text 3 b. Transformers

A transformer is a device that transfers electric energy from one alternating-current circuit to one or more other circuits either increasing (stepping up) or reducing (stepping down) the voltage. Transformers are employed for widely varying purposes; e. g., to reduce the voltage of conventional power circuits to operate low-voltage devices, such as doorbells and toy electric trains, and to raise the voltage from electric generators so that electric power can be transmitted over long distances.

The principal parts of a transformer are: two windings, that are coils, and an iron core. Transformers change voltage through electromagnetic induction; i. e., as the magnetic lines of force (flux lines) build up and collapse with the changes in current passing through the primary coil, current is induced in another coil, called the secondary. The secondary voltage is calculated by multiplying the primary voltage by the ratio of the number of turns in the secondary coil to the number of turns in the primary coil, a quantity called the turns ratio.

A two-winding transformer consists of a closed core and two coils (windings). The primary winding is connected to the voltage source. It receives energy. The secondary winding is connected to the load resistance and supplies energy to the load.

Air-core transformers are designed to transfer high-frequency currents – i. e., the currents used for radio transmission; they consist of two or more coils wound around a solid insulating substance or on an insulating coil form. Iron-core transformers serve analogous functions in the audio-frequency range. They are employed for low-frequency currents.

Impedance-matching transformers are used to match the impedance of a source and that of its load, for most efficient transfer of energy. Isolation transformers are usually employed for reasons of safety to isolate a piece of equipment from the source of power.

XVI. Complete the sentences using the correct variant.

A transformer is applied A transformer consists of The function of the pri-mary winding is The function of the se-condary winding is A transformer with an air core transfers. Iron-core transformers are used Impedance-matching transformers are applied Isolation transformers are employed

to store charge; to prevent the change of energy; to transfer energy; to change the voltage and the current value in a circuit. cores only; the primary and the secondary windings; an iron core and the primary and the secondary windings. to prevent the change of voltage; to supply energy; to receive energy. to receive energy; to decrease the value of charge; to supply energy; to transfer energy. high-frequency currents and low frequency currents; high-frequency currents only. for high-frequency currents; for low-frequency currents. to match the impedance of a source and that of its load; to step down the secondary voltage. for stepping up the primary voltage; for safety in order to isolate a part of machinery from the power source.