Question

Describe the Celsius scale, Fahrenheit scale and Kelvin scale in detail. Give the temperature conversion relations among the different temperature scales.

Accepted Answer

Generally, we use the following three scales of temperature:

(i) The Celsius scale or centigrade scale,

(ii) The Fahrenheit scale, and

(iii) The Kelvin scale

(i) The Celsius scale (or centigrade scale)

This scale was introduced by the Swedish astronomer Celsius and is known after his name. On this scale, the ice point (freezing point of water) is marked as $0 ° C$ and the steam point (boiling point of water) is marked as $100 ° C$ . The interval between the ice point and the steam point is divided into one hundred equal parts. Each division is called one degree Celsius and is written $° C$ . In Greek, ‘Centium’ means $100$ and ‘Gradus’ means steps, both words make it centigrade and later Celsius.

(ii) The Fahrenheit scale

This scale was introduced by Fahrenheit. This scale is generally used for clinical purposes. On this scale, the ice point is marked as $32 ° F$ and the steam point is marked as $212 ° F$ . The interval between the ice point and the steam point is divided into $180$ equal parts. Each division is called degree Fahrenheit and is written as $° F$ .

(iii) The Kelvin scale

This scale was introduced by the scientist Kelvin. It is also called the absolute scale of temperature. On this scale, zero mark (i.e. $0 K$ ) is at the temperature when no molecular motion can occur. This scale has no negative temperature. $0 K$ is the lowest possible temperature. The ice point is marked as $273 K$ and the steam point is marked as $373 K$ . The interval between the ice point and the steam point is divided into $100$ equal parts. Each division of the Kelvin scale is equal to that of the Celsius scale.

Relationship between the three scales of temperature:

1) Between Celsius and Kelvin scales :

We have seen that ice point $0 ° C = 273 K$ and

steam point $100 ° C = 373 K$
$∴$ $t ° C = (273 + t) K$
Thus, by simply adding $273$ to the temperature on the Celsius scale, we get the temperature on the Kelvin scale

2) Between Celsius and Fahrenheit scales:
Ice point $0 ° C = 32 ° F$ and
steam point is $100 ° C = 212 ° F$
Thus, $1$ degree on Celsius scale is equal to $\frac{9}{5}$ degree on the Fahrenheit scale. Hence, the relationship is:

$F = \frac{9}{5} C + 32 o r, C = \frac{5}{9} (F - 32) o r, \frac{C}{5} = \frac{F - 32}{9}$

Describe the Celsius scale, Fahrenheit scale and Kelvin scale in detail. Give the temperature conversion relations among the different temperature scales.

Important Questions on Thermal Properties of Matter

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