Fig. 7. The heating effect of an electric current

 

Let us suppose, now, that a small current is flowing along a thick metal conductor. Under such conditions the only way to discover whether heat has been developed is to make use of a sensitive thermometer because the heating is too negligible to be detected by other means. If, however, our conductor were very thin while the current were large, the amount of generated heat would be much greater than that produced in the thick wire. In fact, one could easily feel it. Thus, we see that the thinner the wire, the greater the developed heat. On the contrary, the larger the wire, the more negligible is the heat produced.

Needless to say, such heat is greatly desirable at times but at some other times we must remove or, at least, decrease it as it represents a needless waste of useful energy. Thus, when heat is developed in a transmission line, a generator or a motor, it is but a useless waste of electric energy and overheating is most undesirable and even dangerous. It is this waste that is generally called “heat loss” for it serves no useful purpose and does decrease efficiency. Nevertheless, one should not forget that the heat developed in the electric circuit is of great practical importance for heating, lighting and other purposes. Owing to it we are able to make use of a large number of appliances, such as: electric lamps that light our homes, streets and factories, electrical heaters that are widely used to meet industrial requirements, and a hundred and one other necessary and irreplaceable things which have been serving mankind for so many years. In short, many of the invaluable electrical appliances, without which life would seem strange and impossible at present, can be utilized only because they transform electric energy into heat.

The production of heat by an electric current is called heating effect. One might also name it light effect provided the heat in the conductor be great enough to make it white-hot, so that it gives off light as well as heat. Take the filament of an electric lamp as an example. We know it to glow because of its heat. By the way, were we able to look inside a hot electric iron, we should see that its wires were glowing too. A similar statement could be applied as well to almost any electric heating devices. All of them give off a little light and a lot of heat. However, it would be quite wrong to decide that electric energy is the only possible source of heat. We are provided with some other sources besides electricity. For example, we can obtain heat from chemical reactions by using chemical energy and from the sun by employing radiant energy. It is quite possible to produce heat by motion and we do get heat from work by making use of mechanical energy. Note that in every above-mentioned case, it is work that produces heat, directly or indirectly. Thus, on the one hand, heat can do work, and on the other, work can produce heat. It is the heat engine that turns heat into work.

 

Exercises

 

Find examples in the text illustrating modality.

Answer the following questions.

1. How can electricity be detected?

2. What are the principal effects of an electric current?

3. Why does the current-carrying wire become red-hot?

4. What does the heat produced per second depend upon?

5. Why is heat, developed in a transmission line, undesirable?

6.  What device turns heat into work?

7. What do we call a heating effect of an electric current?

8. When does the conductor become white-hot?

9. What takes place inside any electric heating device?

10. What sources of heat do you know?

 

Define the meaning of the prefixes in the following words, translate them.

Irreplaceable, supernatural, overloaded, reaction, invaluable, discharge, indirectly, outstanding, semiconductor, impossible.

 

Translate the following sentences.

1. It was in 1800 that Volta first produced a continuous current.

2. It is the thermometer that measures the temperature of a substance.

3. It was Lomonosov who stated that heat phenomena were due to molecular motion.

4. It is the production of heat by an electric current that is called heating effect.

5. It is the ampere that is the unit of current.

6. It was Popov who was the inventor of the radio.

 

Ask each other questions.

A

1. If it is possible to convert electric energy into heat.

2. If we can obtain heat from the sun by employing radiant energy.

3. If he/she is able to look inside a hot electric iron.

4. If it is desirable at times to remove heat.

5. If heat decreases efficiency.

 

B

1. What the three principal effects of an electric current are.

2. How the current, passing along the wire, can be detected.

3. Where the electrical appliances are used.

4. When overheating is most undesirable and even dangerous.

5. What phenomenon highly interested Ampere.

 

6. Translate the following sentences paying special attention to the words in bold type.

 

1. What is your teacher’s name? Can you name the kinds of electric current?

2. There is a great need for research methods. I need an English book on physics.

3. There are many things that heat can do. In effect, the electric current passing through the wire will heat that wire.

4. We cannot detect the flow of electrons by our physical senses.

5. If the switch were turned on, the electrons would flow in a circuit.

6. Many rivers flow into the sea.

 

7. Use the conjunctions either... or, neither... nor, both... and in sentences given below.

Model: He will read or write.

        He will either read or write.

        He will neither read nor write.

        He will both read and write.

 

1. She speaks English or German.

2. He or she can translate this article.

3. We’ll go by bus or by tram.