# Man's physical universe

210 PHYSICAL LIMITATIONS HAVE BEEN OVERCOME

Charles' Law Deals with Temperature-volume Relationships.

The expansibility of gases is

another property of gases stated as a

law, named after Charles, who first observed that under constant

pressure the volume of a gas is very nearly proportional to the absolute

temperature.

This property is likewise familiar qualitatively, because, as most

people have observed, the volume of a gas in a closed container will

expand when heated, provided that it is capable of expansion. Thus

the sides of a gasoline tin will bulge out and a balloon will swell to the

bursting-point as it is heated. The quantitative aspects of this law

are not so well recognized, inasmuch as the absolute-temperature scale

is unfamiliar. The three common temperature scales are shown in

Fig. 68.

It was observed that the volume of a given weight of gas would

decrease 1/273 for each degree of decrease in temperature below 0" C.

Water Boils

Water Freezes

Absolute Zero

op op OA If the temperature were lowered

@ @ @

273° C, the decrease in the volume

212°

32°

-459.4° -273°

373°

273°

of the gas would thus produce zero

volume if the gas did not condense

earlier. (All gases do condense above

absolute zero.) This temperature,

called absolute zero, is the lowest

temperature theoretically possible

to obtain. It has been approached

experimentally within a small fraction

of a degree.

Standard Temperature.

In making many measurements,

the results must be expressed at

the same temperature for purposes

of comparison. The standard reference

temperature is 0° C.

Temperature measurements depend

upon the measurement of the

Fig. 68. The three temperature

scales.

amount of expansion of gases or

liquids, such as mercury or alcohol, in thermometers. Temperatures

may be measured by the electric current produced when one of two

metals in contact with each other (a thermocouple) is heated. In the

case of the resistance thermometer, the temperature is measured by

the change in the electrical resistance of a coil of wire in response to

changes in temperature. Inasmuch as electrical resistance can be

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