Version 7 Refrigerator

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As you know, whenever a gas turns into a liquid, heat is invariably developed. Similarly, heat is required to turn a liquid into a gas. Whenever a liquid is vapourised, heat is taken from the immediate surroundings. When ether evapo­rates on your finger, it turns from a liquid to a gas and takes heat from your finger in this process. If there were enough ether on your finger and a constant supply of heat could be, kept, the rapid evaporation would cool your finger so much that it would become frozen. This is the principle the modern refrigerator is based upon.

Some gases are easily liquefied and when liquid, they are easily turned back into the gaseous state. Sulphur dioxide is pumped under pressure until it liquefies. The liquid sul­phur dioxide is pumped into a coil of small pipes which sur­rounds a number of trays filled with water. As soon as the liquid enters this coil, it passes through a nozzle which creates a very fine spray, causing it to expand. In expanding this liquid becomes a gas again and when expanding, it takes up a considerable amount of heat from the immediate surround­ings.

Quiz

for the third-year students, 5^th term (EP, ES)

Prepared by A.V.Kosobokova

Version 8 Boiling

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If we heat some water in an open glass container, we can see that evaporation goes on from the top surface. This evap­oration is indicated by the clouds forming where the vapour mixes with the colder air and condenses. We find that the temperature of water gradually rises until the thermometer registers 100°C. A little before this point is reached, bubbles appear on the sides of the container. They consist partly of gases driven from liquid and partly of water-vapour, for evap­oration is directed into the bubbles. Water is said to boil when vapour is formed both at the bottom of the container and at the top of it. The motion of the boiling water is caused by the bubbles of vapour rising through the water. The tem­perature of the boiling water is constant. This temperature is known as the boiling point of the liquid.

The boding point of a liquid is the temperature at which it boils under some given pressure. When this point has been reached, further heating does not increase the temperature of the liquid but only changes it into steam.When water boils in a container, we say that we see steam coming out of it. In fact, what we see is not steam at all but fine water particles.

Quiz

for the third-year students, 5^th term (EP, ES)

Prepared by A.V.Kosobokova

Version 9 Structure of the Atom

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The atom is the basic partible of all matter. All solids, gases, and liquids are composed of atoms.

For a time the atom was considered to be indivisible but then it has been found that the atom in its turn can be divid­ed into many different components.

In dividing the atom, man releases forces of great magni­tude. These are forces that bind the central core of the atom. This central core – the nucleus – is extremely small in di­ameter.

The nucleus of the atom is of a highly complex structure. It is the three main components of the atom that we shall deal with below. These are called protons, neutrons and elec­trons.

The proton carries a positive charge of electricity, the number of protons in the nucleus determining the element that the atom forms.

For example, if the nucleus has a single proton, then it will form the gas hydrogen. If 92 protons are present, the element will be uranium and so on. In short, if the number of protons in the nucleus is known, the element can be found out at once.

Quiz

for the third-year students, 5^th term (EP, ES)

Prepared by A.V.Kosobokova