Transmission of heat

Heat can be transmitted by conduction, metals being the best conductors; convection, which is taking place only in liquids and gases; and radiation.

What is conduction? When one end of an iron rod is held in flame, the other end of the rod will soon be too hot to be held comfortable. In some way, the heat is conducted, or led, from one end of each solid to the other end. The molecules of the rod which are adjacent to the flame receive some of this heat energy, which they transmit along the rod to other molecules. Such transmission of heat from molecule to molecule is called conduction. Metals generally are much better conductors of heat than wood or stone.

What is convection? When the portion of water near the bottom of a vessel is heated, it expands and becomes less dense. The denser water from the opposite side of the vessel flows across and pushes up this less dense water thus setting up convection currents. Convection currents may be set up in either liquids or gases by unequal heating. By means of such currents heat is transmitted by the movement of the heated masses.

What is radiation? Radiant heat is the name given to heat in the form of rays. A hand held in front of a fireplace is quickly warmed by radiation. We receive heat from the sun the same way. This heat radiation is probably due to the internal motion of the atoms and molecules of the heat-producing body, and travels through space as a wave. Heat radiation is one of several types of wave motion studied in physics, called electromagnetic waves.

Heat radiation is not heat itself, but the absorption of heat radiation produces heat in the absorbing medium. Thus: 1) Radiation can travel through a vacuum. 2) Radiant heat warms only objects on which it falls and which absorb it; it does not heat the “medium” through which it passes.

How can heat be transmitted? Where does convection take place? What is conduction of heat? What is radiant heat? Trough what can radiation travel? What does radiant heat warm?

Ex.1. Make up the questions to this text.

Ex. 2. Copy these sentences selecting the proper word in the blank

1. … take place only in liquids and gases. (radiation, convection, conduction). 2. Transmission of … from molecule to molecule is called conduction of heat. (light, sound, heat). 3. Radiation can … through a vacuum (absorb, travel, warm). 4. Convection currents may be set up by … (transmitting, falling, heating).

Ex. 3. Make up sentences using the word combinations

Decompose, discover, to be decomposed, to be found, to be transformed, travel

Convection, one end of an iron rod, through a vacuum, through space as wave.

Transmission of heat, transmitted by conduction, iron rod, heat energy, bottom of a vessel, becomes less dense, flows across, pushes up, radiant heat, internal motion, absorbing medium.

Ex. 4. Copy these sentences putting “radiation”, “electric”, “could”, “carries”, “gases”, “motion”, “vacuum”, “transferred”, “direction” in the blanks

1. Heat can be … by material substances: by solids, liquids and … 2. Heat can also be transferred by wave …, even across a … 3. This is called … 4. Hold your hand under an unlighted … bulb, palm upward. 5. The heat … not have reached your hand by conduction or convection. 6. Radiation … heat in every … from the source.

Ex. 5. Translate into English.

- Теплота – это форма энергии. Обсудим, какими способами она может передаваться.

- Она может передаваться различными способами. Например, с помощью проводимости.

- Верно. Это способ передачи тепла. Кстати, что является лучшими проводниками тепла?

- Металлы. Они передают тепло от молекулы к молекуле. Говоря, что они проводят тепло.

- Вы правы. А что Вы знаете о конвекции?

- Это тоже способ передачи тепла. Оно передается благодаря движению нагретых масс.

- Радиация – это тоже способ передачи теплоты, не так ли?

- Да, конечно.

Ex. 5. Substitute the infinitive by the proper form of the verb (active or passive)

When heat (to add) to a substance, that substance (to get) hotter and its temperature (to rise). If heat (to remove), the temperature (to fall). The fact that such temperature (to change) can be brought about (to show) that heat exchanges (can take place) and that heat (can be transferred) from one region to another. There (to be) three ways in which this transmission (can occur).

Ex. 6. Put the verbs in brackets into the proper tenses.

1. If the Moon (be attracted) by the Earth, it (move) along a straight line. 2. If we (measure) the time of arrival of the particle at each of many points along the path between A and B we (describe) the motion in detail. 4. If every point on the earth's surface (be rotting) at the same speed, the earth (be) perfectly spherical. 5.. If. you (make) an experiment correctly you (get) a convincing result. 6. If we (repeat) the experiment with a different force we (find) the acceleration. 7. If you (put) your hand on the block it (exert) a force. 8. If there (be) no accelerator it (be) impossible to explore the subatomic world. 9. If the known part of the universe (have) the size of the earth, how large (be) the earth?