Read and translate the text

Meters

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 pointand 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.

3. Complete the sentences using the correct variant:

1. The ammeter is

a) a common meter.

b) an uncommon meter.

2. In order to measure the value of current

a) the ohmmeter is used,

b) the voltmeter is used.

c) the ammeter is used.

3. A meter has

a) positive terminals only.

b) negative terminals only.

c) positive and negative terminals.

4. When the ammeter is used

a) the circuit should be opened.

b) the circuit should not be opened.

5. The ammeter should be connected

a) in series,

b) in parallel.

6. One should take into consideration that

a) the positive terminal should be connected to the negative terminal.

b) the positive terminal should be connected to the positive terminal of the source.

Pair work. Put these questions to your groupmate. Let him/her answer them.

1. What is the ammeter used for?

2. What is the voltmeter used for?

3. What is the ohmmeter used for?

4. What terminals does a meter have?

5. Should the measured circuit be opened when the voltmeter is used?

6. Should the measured circuit be opened when the ammeter is used?

7. In what way should the voltmeter be connected to the circuit?

8. In what way should the ammeter be connected to the circuit?

9. What is the difference between a voltmeter and an ammeter?

10. What common meters are used to measure the values in a circuit?

Практическое занятие 5. Резисторы

Lesson 5. Resistors

1. Read and learn the words:

capacity - емкость

power - мощность

heat - теплота, нагрев

rate - скорость, степень

to produce - производить

to change - менять(ся)

to vary - варьировать(ся)

low - низкий

high - высокий

fixed – постоянный

any - (зд.) любой

variable - переменный

the (more)... the (more) чем (больше)... тем (больше)

2. Translate into Russian using чем... тем:

1. The more one studies nature, the better one knows its laws.

2. The longer one learns, the more one knows.

3. The higher the atmosphere, the less is its pressure.

4. The heavier the object, the more work one has to do in order to lift it.

5. The greater the number of free electrons in any metal, the higher is its

conductivity.

3. Translate into Russian. Mind no.

1. There is no energy in this machine.

2. No charges move through an open circuit.

3. No material is a perfect conductor of electricity.

4. No electric machinery is used without protection.

5. No special material is needed in this case.

Read and translate the text.

Resistors

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 o f 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. A resistor is rated as a I-W resistor if its resistance

equals 1,000,000 ohms and its current-carrying capacity equals I/1,000,000 amp, since P = E x I = IR x I = I²R where P - power is given in watts, R - resistance is given in ohms and I - current is given in amperes. If a resistor has a resistance of only 2 ohms but its current-carrying capacity equals 2,000 amp, it is rated as a 8,000,000-W resistor. Some resistors have a constant value - these are fixed resistors, the value of other resistors may be varied - these are variable resistors.

5. Complete the sentences using the correct variant:

1. A resistor is used

a) to measure the resistance.

b) to reduce the current.

c) to change the resistance.

d) to produce IR voltage drop.

2. When current passes through a resistor

a) its temperature drops.

b) its temperature rises.

3. Resistors are rated

a) in ohms.

b) in volts.

c) in watts.

4. Power is given

a) in amperes.

b) in watts.

5. Fixed resistors have

a) a constant value.

b) a variable value.

6. The value of a variable resistor

a) is fixed.

b) is varied.

7. A two-ohm resistor rated as a 8,000,000-W resistor

a) has a current-carrying capacity equal to 2,000 amp.

b) has a current-carrying capacity equal to 200 amp.

Pair work. Put these questions to your groupmate and let him/her answer them.

1. What is a resistor used for?

2. When does the temperature of a resistor rise?

3. What element is used to change the value of voltage?

4. How are resistors rated?

5. What types of resistors do you know?

6. When does a resistor get open?

7. What does an open resistor result in?

8. What is the difference between a fixed resistor and a variable resistor?

9. How much is the current-carrying capacity of a two-ohm resistor?

10. What resistors have a variable value?

Практическое занятие 6. Гальванические элементы

Lesson 6. Electric Cells

1. Read and learn the words:

Cell - элемент

output - емкость, мощность

bulb - электрическая лампа

to light - зажигать, освещать

to increase - увеличиваться), возрастать

to substitute - заменять

...and so on - и так далее

Read and translate the text.

Electric Cells

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.

3. Complete the sentences using the correct variant:

1. A cell is used

a) to increase the voltage output.

b) to reduce the current capacity.

c) to supply electric energy.

2. The terminals of a cell are used

a) to conduct current.

b) to increase voltage.

c) to connect the battery to a circuit.

3. When cells are connected in series

a) all the positive terminals are connected together.

b) all the negative terminals are connected together.