Laboratory Exercises
9. Listen and read the following words paying attention to the pronunciation of "ее", "ea", "at", "qu":
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degree, been, see, need, steel, keep, heat, deal, release, steady, measure, contain, attain, raise, remain, liquid, require, equal, quantity
10. Listen and repeat in pauses:
A calorimeter is a device to measure heat. It is made of a highly polished copper can. It is suspended inside a; larger can or jacket. A small can contains water to transfer heat of a hot body having been placed in it. The rise in temperature of water is measured with a thermometer. The outer can minimizes loss of heat from the calorimeter to its surroundings by conduction, convection and radiation.
11. Listen to these questions on the above text and answer them:
1. What is a calorimeter? 2. What is it made of? 3. Where is a small can suspended? 4. What does it contain? 5. What does the outer can minimize?
12. Ask questions using the model.
Model: A calorimeter is used in heat experiments.
Where is a calorimeter used?
1. A small can is suspended in a larger can or a jacket. 2. A hot body is placed into water inside a small can. 3. A calorimeter is opened at the top. 4. It is closed at the bottom. 5. It is polished on the outside.
13. Listen to this short dialogue and learn it by heart:
- Let us speak about a calorimeter. What is it?
- It is a metal container of simple shape. Do you know what metal it is made of?
- If I am not mistaken, it is made of copper, isn't it? — Yes, it is. You are quite right. It is usually made of
copper or aluminium. Do you use a calorimeter in your work?
- Certainly, I do. We make some heat experiments in which it is necessary to use a calorimeter.
- Of course, heat changes can be studied in it.
14. Say this in English:
1. Теплота — это форма энергии. 2. Тепло передается проводимостью металлов, конвекцией жидкостей и газов
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и излучением. 3. Тепловые величины измеряются калориями. 4. Кало-риметры используются для определения теплоты нагретого тела. 5. Калориметр сделан из хорошо отполированного медного сосуда, в который налита вода. Нагретый предмет помещают в воду. 7. Тем-пература воды измеряется термометром.
15. Suggested topics for oral narration:
1. What is the difference between heat and temperature? Define two heat units in common use and show the relationship between them.
2. Describe the construction of a calorimeter.
3. Tell about the process of measuring heat in a calorimeter.
Additional Material
Read the text and describe the property of a vacuum flask to keep liquids hot.
The Vacuum Flask
The vacuum flask is known to most of us as the Thermos flask, which is the trade name used by a large manufacturing firm. Originally, it was devised for the purpose of storing liquefied gases. Liquid oxygen, for example, boils at the very low temperature of —183 C, so that if it is placed in an ordinary flask it rapidly boils away. It is necessary therefore to keep it in a vessel through which heat cannot pass.
The vacuum flask consists of a double-walled glass vessel having a vacuum between the walls. Both walls are silvered. No heat can enter or leave the inner flask by conduction or convection across the vacuum. A certain amount of heat can be gained by the flask through radiation, but this is reduced to a minimum on account of the silvering. In addition there will be a little heat transmitted by conduction through the thin glass walls at the neck, and through the poorly conducting cork. The sum total of this heat transfer is so very small that a cold liquid inside remains cold for a very long period.
The vacuum flask is equally suitable for keeping liquids hot. There must be few people indeed who have not enjoyed the advantage of having a vacuum flask filled with hot tea or coffee when out on a picnic.
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UNIT 11