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Welcome to our Physics lesson on Units of Temperature, this is the second lesson of our suite of physics lessons covering the topic of Temperature. The Zeroth Law of Thermodynamics, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.
Anders Celsius, a Swedish scientist introduced (in the eighteenth century) a practical method of thermometer calibration. He used the freezing and boiling points (temperatures) of water as a lower and upper fixed points respectively and then he decided to divide the range of temperatures between these two fixed points in 100 equal parts. Each division is called 1-Celsius degree (1°C)and such a way of thermometer calibration is known as Celsius Scale. Obviously, such a calibration can be extended even beyond these two fixed points as we know that in winter air temperatures can go below zero or melting process of metals needs temperatures much higher than 100°C.
On the other hand, Daniel Gabriel Fahrenheit, a German scientist, used the temperatures in the coldest and the hottest days in his country to calibrate thermometers. In this way, he invented the Fahrenheit Scale. The conversion formula between Celsius and Fahrenheit scales is:
The weather forecast shows a value of 86° F for the next day. What is the corresponding value in Celsius degree?
From the formula
we obtain after substituting the values:
86 = 1.8 × t (°C) + 32
1.8 × t (°C) = 86 - 32 = 54
t (°C) = 54 / 1.8
t (°C) = 30°C
However, the official SI unit of temperature is none of the above but Kelvin Scale. It is named after the Lord Kelvin, alias William Thompson, the Scottish famous scientist. Kelvin degree is the SI unit of temperature as it offers a great advantage compared to the other units: it has only positive (or zero) values because the lower fixed point of this scale refers to the lowest temperature in the universe, i.e. the temperature in which particles of matter stop vibrating around their equilibrium positions. When measured in Celsius degree, this minimum temperature is equal to -273.16°C. Therefore, we can write:
or more generally,
The division method is the same in both Celsius and Kelvin degrees, only the lower fixed points are different. This means an increase in temperature by 5°C for example, represents an increase in temperature by 5 K as well.
Convert the following temperatures into the required ones:
a) Given that
When converted this value into Kelvin degree, it becomes
b) First, let's convert the temperature from Kelvin to Celsius Scale. Thus, given that
we obtain, after substitutions for the temperature in Celsius scale,
Remark!
Unlike in the other two scales, in Kelvin scale temperature is denoted by capital T instead of t. Also, the symbol of degree (°) is not written in Kelvin scale.
You have reached the end of Physics lesson 13.1.2 Units of Temperature. There are 3 lessons in this physics tutorial covering Temperature. The Zeroth Law of Thermodynamics, you can access all the lessons from this tutorial below.
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