10.1 Answer the following questions

1. What is magnetism?

2. What is called the North (South) pole?

3. When do poles repel each other?

4. When do poles attract each other?

11 Batteries produce electricity

A battery produces electricity using two different metals in a chemical solution. A chemical reaction between the metals and the chemicals frees more electrons in one metal than in the other. One end of the battery is attached to one of the metals; the other end is attached to the other metal. The end that frees more electrons develops a positive charge and the other end develops a negative charge. If a wire is attached from one end of the battery to the other, electrons flow through the wire to balance the electrical charge. A load is a device that does work or performs a job. If a load––such as a lightbulb –– is placed along the wire, the electricity can do work as it flows through the wire.

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11.1 Find and read all the international words in the text.

12 Direct current and alternating current

We know that current is the flow of electricity through a circuit. There are two main types of current: direct and alternating. When electrons flow in one direction only, the current is called a direct current. When electrons flow first in one direction and then in another in a periodic manner, the current is called an alternating current. An alternating current is a current that changes its direction of flow through a circuit in a periodic manner. Alternating current flows in cycles. The number of cycles per second is termed the frequency of current. In a 60-cycle alternating current circuit, the current flows in one direction 60 times per second and in the other direction 60 times per second.

A standard frequency has a great advantage since different electrical systems can be interconnected.

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12.1 Answer the questions

1. What is current?

2. What types of current do you know?

3. What type is termed a direct current ( an alternating current)?

4. In what manner does an alternating current flow?

5. What is frequency?

12.2 Test. Choose the correct variant

1. Direct current …

1. changes its direction of flow

2. flows in one direction

2. The frequency of the circuit is …

1. the number of cycles per minute

2. the number of cycles per second

3. A standard frequency has …

1. great advantages

2. disadvantages

13 Conductors

According to their conductivity all materials are divided into conductors, insulators and semiconductors. Conductors allow electricity to pass through them; insulators do not. Conductors are materials having a very high conductivity. A conductor owes its conducting powers to the presence of free electrons which have broken away from their atoms. The most common of them are metals (copper, aluminium, steel and others), carbon and electrolytes. Their coefficient of resistance is different. Copper, for example has a positive coefficient while carbon has a negative coefficient of resistance.

According to their resistivity, conductors are divided into two groups; the first includes materials with low resistivity; copper, aluminium and others. These metals are used to produce wire conductors due to their high mechanical strength. The second group includes materials with high resistivity: one of these is nichrome. Due to its good heat resistance, nichrome is used to produce heaters. Carbon is commonly used to produce electrodes and brushes for electric machines.

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