VII. Complete the sentences using the correct variant.

1. The ammeter is a) a common meter

b) an uncommon device

2. In order to measure the value of current a) the ohmmeter is used

b) the ammeter is used

3.For measuring the potential difference a) a voltmeter is used

between any two points in a circuit b) an ammeter is used

c) a galvanometer is used

4. The ammeter should be connected a) in series

b) in parallel

5. To measure small currents a) a galvanometer is used

b) an ammeter is used

c) a voltmeter

Speaking

VI. Give an English definition for the following terms:

1. ammeter

2. galvanometer

3. voltmeter

Resistance and Resistivity

Reading

I. Read the following words:

material, temperature, copper, silver, aluminium, honour, physicist, standard, column, proportional diameter.

II. Read and translate the text.

Every material offers some resistance to the flow of electric current through it. The resistance of a conductor depends on its material. It also depends on its temperature. Materials change the value of resistance with change in their temperature. Different materials also have different melting points. Good conductors, like the metals copper, silver, and aluminium, offer very little resistance, while non-conductors, like glass, wood and paper, offer a very high resistance. The resistance of copper, silver, and aluminium, is rather high.

Resistance of conductors and their resistivity have different units. The unit by which resistance is measured is called the ohm, in honour of the German physicist Ohm. The unit of resistance is the ohm while the init of resistivity is the ohm.m. The standard international ohm is defined as the resistance offered to a steady electric current by a column of mercury 1sq. mm in cross-section and 106.3 cm long at a temperature of 0.

When an electric current flows through a resistance, there is a loss of energy as well as a loss of voltage or electric pressure. Both these losses are directly proportional to the amount of resistance.

The larger the diameter of the wire, the smaller the resistance is and, hence, the more current can flow through it. The resistance of a conductor depends not only on its diameter and length but also on the kind of substance it is made of and on its temperature.

Vocabulary

III. Remember these words:

glass, to melt, unit, to define, mercury, cross-section, loss, to flow, amount.

Grammar

IV. Translate the following sentences.

1. Some materials conduct electricity readily provided light falls on them or their temperature is raised.

2. The addition of heat does not increase the weight of metal, however, the combination with air does increase its weight.

3. If the magnetic circuit consisted of non-magnetic material, the field would be proportional to the current.

4. It is possible to find out the resistance of the conductor at any given temperature, provided the resistance at one temperature is known.

5. The pipe had a small cross-section area and the water flow per second was also small.

6. It is in a transmission line that one should use as good a conductor as possible.