Physics A2 · Temperature. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
To measure temperature we use a physical property that changes with temperature. Examples are the density of a liquid, the volume of a gas at constant pressure, the resistance of a metal and the e.m.f. of a thermocouple. A thermometer is calibrated at two fixed points and the property is assumed to change linearly between them.
Different properties do not change in exactly the same way, so two such thermometers can disagree slightly between the fixed points. The thermodynamic scale, in kelvin, avoids this: it does not depend on the property of any particular substance.
Its zero, 0 K, is absolute zero, the lowest possible temperature. No temperature in kelvin is negative.
Students add 273 to a temperature change. Only add 273 to a temperature; a rise of 30 °C is a rise of 30 K. And 'doubling the temperature' means doubling the kelvin value, not the Celsius value.
Answer: 35 °C, which is about 308 K.
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