Question

What are the lower and upper fixed points of the Celsius scale?

Answer 1

Hint: A temperature scale is defined by choosing two fixed points whose values are easily reproducible. In the case of the Celsius scale, the lower point is the melting point of pure ice at normal atmospheric pressure and the upper fixed point is the boiling point of pure water at normal atmospheric pressure $\left( 1atm \right)$.

Complete step by step answer:
A temperature scale is a unit of measurement to measure the temperature. Usually, scales of temperature are developed by first fixing two points, the upper limit and the lower limit of the scale. The temperature values of these two limits must be easily reproducible by some natural phenomenon. Then the scale is calibrated by making equal divisions between these two limits.

In the case of the Celsius (symbolized by $^{0}C$) scale, the upper fixed point is ${{100}^{0}}C$ .

This is the boiling point of pure water at normal atmospheric pressure ($1atm$ or $1.01325\times {{10}^{5}}Pa$). This is easily reproducible since pure water at $1atm$ The lower fixed point is ${{0}^{0}}C$. This is the melting point of pure ice at normal atmospheric pressure $\left( 1atm \right)$. This is also easily reproducible since pure ice at $1atm$ always freezes at ${{0}^{0}}C$.

Between ${{100}^{0}}C$ and ${{0}^{0}}C$, there are 100 divisions each of ${{1}^{0}}C$. Thus, any instrument can be easily calibrated according to this scale.

Therefore, the lower and upper fixed points of the Celsius scale are ${{100}^{0}}C$ and ${{0}^{0}}C$ respectively.

Note: There are also other scales of temperature such as the Fahrenheit scale $\left( ^{0}F \right)$ and the Kelvin $\left( K \right)$ scale. The Kelvin scale is also known as the absolute scale of temperature and is the standard scale. The SI unit of temperature is Kelvin $\left( K \right)$. $0K$ is known as the absolute zero temperature. The Kelvin scale does not have a negative range whereas the Fahrenheit and Celsius scales do.