Question

Absolute scale of temperature is known as _______ (Celsius scale, Kelvin scale)

Answer 1

Before we get to understand the measurement of temperature, it is important to know the definition of temperature.
Temperature is defined as the degree of hotness and coldness of a system, which primarily, indicates the direction of heat transfer between one or more thermodynamic systems.

Complete step-by-step answer:
The temperature is different from heat. The heat is defined as the energy which is transferred across the system which can change the net total of the internal energy of the system whereas, the temperature is a quantity that manifests out of the heat energy, that measures the degree to decide the direction and the extent of transfer of heat energy from one system to another.

The temperature is measured by a device known as a thermometer. It is a device which contains a liquid such as alcohol or mercury is a small bulb, which expands into a small vertical capillary column, which has several graduation markings depending on the scale used to measure the temperature.

The graduations which are marked on the thermometer is based on a standard scale of measurement. Historically, there have been several scales of temperature, but the most common and the widely used scales of temperature are only 3: i) Celsius scale ii) Fahrenheit scale iii) Kelvin scale
i) Celsius scale : Also known as the centigrade scale, the Celsius scale consists of 100 divisions starting from ${0^ \circ }C$ which is the first reference point called the freezing point of water and the highest is the second reference point, the boiling point of water which is ${100^ \circ }C$. This scale is widely used in almost all countries except the USA, for commercial purposes like meteorology.

ii) Fahrenheit scale : This scale has the first reference point, the freezing point of water at ${32^ \circ }F$ and the second reference point, the boiling point of water at ${212^ \circ }F$. Also, every ${1^ \circ }C$ rise in the temperature corresponds to $1 \cdot {8^ \circ }F$ change in the Fahrenheit cycle. This scale of temperature is currently in use only in the United States of America for commercial purposes like meteorology.

iii) Kelvin scale : Unlike the above two scales of temperature that are based on the freezing and boiling points of water, this scale of temperature is based on the Boltzmann’s constant, denoted by $k$.
One kelvin is defined as the change in the temperature when the heat energy equal to the Boltzmann’s constant i.e. $1 \cdot 38 \times {10^{ - 23}}J$ is transferred to or from the system.
In terms of Celsius scale, $1K = 273 \cdot {15^ \circ }C$
This scale is considered as the standard for every scientific calculation and the unit kelvin is designated as the one of the 7 base units by the International System of Units. Hence, this is called the absolute scale of temperature.

**Thus, the absolute scale of temperature is the kelvin. **

Note: Before the advent of the kinetic theory of gases by pioneers like Boltzmann, the absolute scale was based on the thermodynamic terms. The thermodynamic temperature was considered absolute. But, after the Maxwell-Boltzmann distribution theory and the statistical definition of the term entropy got introduced, the basis for defining the absolute scale changed to the kinetic theory of gases, as explained in this answer.