Current Flow

In order for current to flow, two conditions must be met¹. First, there has to be a potential difference (voltage) to force the current to flow and, second, there must be a continuous circuit (circle) for the current to flow around. When we start to look at circuits, we see that there are different combinations: series circuits, parallel circuits and parallel-series circuits.

If a number of resistors are connected together end to end and then connected to a battery, the current can only take one route through the circuit. This type of connection is called a series circuit (Fig. 1).

Fig. 1. Series circuit

 

If a number of resistors are connected together so that there are two or more routes for the current to flow, as shown in
Figure 2, then they are said to be connected in parallel. In this type of connection the total current splits up and divides itself among the different branches of the circuit. However, note that the pressure pushing electrons along (voltage) will be the same through each of the branches. Therefore, any branch of a parallel circuit can be disconnected without affecting the other remaining branches.

Fig. 2. Parallel circuit

 

A series/parallel circuit combines the series and parallel circuits as shown in Figures 1 and 2. To calculate the total resistance in a combined circuit, we must first calculate the resistance of the parallel group. Then, having found the equivalent value for the parallel group, we simply treat the circuit as being made up of ² series connected resistors and now add this value to any series resistors in the circuit, thus giving us the total resistance for the whole network.

 

Notes

¹ to meet conditions – виконувати умови

² treat the circuit as being made up of – розглядати коло як таке, що складається з

 

2. Now read the text once again looking up any word you do not understand in a dictionary and answer the following questions.

1. What two conditions must be met in order for current to flow?

2. What is a series circuit?

3. What is a parallel connection?

4. What does a series/parallel circuit combine?

 

3. Under the table there are six statements about circuits. Sort them into two groups under the following headings:

 

Series circuits	Parallel circuits

a. There is only one path for the current.

b. There are several paths for the current.

c. The current is not the same at all points in the circuit.

d. The current is the same at all points in the circuit.

e. The potential difference across each component is the same.

f. The potential difference across each component is usually different.

 

Pronounce correctly

 

4. Read the following words with the letter s:

[s] test, density, lists, pass, sun, start, see, some, scale, false, site;

[z] visit, position, resistor, branches, as, chosen, these, phase;

[] usually, visual, cohesion, adhesion, television, casual, Asia, corrosion.

 

5. Read the words given below paying special attention to the ending –tion.

Isolation, installation, protection, deflection, combination, inspection, connection, explanation, friction, condition, position, production, motion, definition, information, reflection, proportion.

 

Increase your vocabulary

 

6. Find these words and word combinations in the text and try to remember them:

 

a number of branch combine connect continuous divide network

parallel circuit route series circuit show (showed, shown) split up (split, split) total value

Suffixes say a lot

7. What part of the speech are these words? Translate them.

Temperature, agriculture, pressure, enclosure, manufacture, closure, composure, miniature, measure, structure, pleasure.

 

8. Complete the following sentences using the words from exercise 7.

1. Atmospheric ____ is high today.

2. The ____ of this series/parallel circuit is complex.

3. We are specialized in electrical engineering and computer technologies for ____.

4. The ____ is given in centimeters.

5. The ____.of energy saving devices is growing rapidly.

6. He can keep his ____.

7. It gives me great ____ to present the next speaker.

 

9. Match the words in A with the words which have similar meaning in B.

A. Among, to force, to split up, to affect, to combine, value, to treat, whole.

B. Quantity, to influence, total, to unite, to consider, to make, between, to divide.

 

10. Choose the word which best completes each sentence.

 

a. Measure b. measurement

c. measurable d. immeasurable

 

1. In the MKSA (meter-kilogram-second-ampere) system of units, length, mass, time and current are the fundamental ____ quantities. 2. Throughout history, many official systems of ____ have been used. 3. His contribution is ____, almost impossible to put into words. 4. To solve this problem it is necessary to ____ the resistance in the circuit.

 

e. Combine f. combination

 

5. Their invention is the ____ of power engineering and computer technologies. 6. These chemicals ____ with air to form a liquid.

11. Complete the passage using the following words and word combinations.

 

a. provides b. low potential c. generator d. consist of e. light and heat f. current flow

g. which supplies electrical energy h. electric circuit i. conducts j. converts k. switch l. in order to

 

Circuit Elements

Current moves from a point of high potential energy to a point of (1) ____. It can only do so if there is a path for it. This path is called an (2) ____. All circuits contain four elements: a source, a load, a transmission system and a control.

The source (3) ____ the electromotive force. This establishes the difference in potential which makes current flow possible. The source can be any device (4) ____. For example, it may be a (5) ____ or a battery. The load (6) ___ the electrical energy from the source into some other form of energy. For instance, a lamp changes electrical energy into (7) ____. The load can be any electrical device.

The transmission system (8) ____ the current round the circuit. Any conductor can be part of a transmission system. Most systems (9) ____ wires. The metal chassis of many electrical devices are used (10) ____ conduct current. Similarly, the body of a car is part of its electrical transmission system. The control regulates the (11) ____ in the circuit. It may limit the current, as does a rheostat, or interrupt the current, as does a (12) ____.

 

12. Put in order to or so that into the gaps.

1. ____ know which tool to use for which job, it is important to be familiar with the basic types of electro-technical systems. 2. He arrived early ____ he could work alone. 3. I always go to the library ____ find information. 4. Compressor, gas turbine and alternator (генератор змінного струму) are mounted on the same shaft ____ a part of mechanical power of the turbine can be utilized for the operation of the compressor. 5. I came here ____ get a good education. 6. The solar power station uses the Sun’s energy ____ produce electricity. 7. Several resistors are connected in parallel ____ there are several routes for the current to flow.
8. We need an electromotive force ____ drive electrons through a conductor. 9. Students gain their practical training at a farm ____ they improve their professional skills. 10. You should use Ohm’s law ____ solve this problem

 

Word range

13. Which sentence best illustrates the use of the word in italics taken from the text?

1. Therefore any branch of a parallel circuit can be disconnected…

a. Power engineering is a branch of electrical engineering.

b. A new branch appeared in the tree.

c. You should understand current division in a two-branch parallel circuit.

2. A series/parallel circuit combines the series and parallel circuits as shown in Figures 1 and 2.

a. He always combines the forces of all the team members.

b. Combines or combine harvesters are machines that both reap and thresh grains.

c. Hydrogen combines with oxygen to form water.

 

Revise your grammar