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The Celsius scale was introduced by the Swedish Physicist, Engineer, and Astronomer Anders Celsius. Celsius Scale is also called centigrade scale. Celsius temperatures obey a system of relative scale, rather than an absolute system of scale or ratio.
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Keyterms: Celsius scale, Celsius, centigrade scale, relative scale, absolute system, Scale, ratio, boiling point, freezing point, heat energy
Read Also: Thermodynamics
Celsius Scale
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The Celsius scale is defined as the temperature scale based on 100° for the boiling point, and 0° for the freezing point of water. Initially, the temperature of 1000° was used to denote the freezing point of water and 0° for the boiling point of water. Later the values of the temperature were inverted to 0° and 100° denoting the freezing and boiling point of water respectively. This celsius scale is used worldwide.
Notes on Celsius Scale
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The Celsius scale follows the relative interval or scale instead of an absolute system of a ratio or scale. The Ratio scale type is used for the calculation of the weight or distance. The change in the weight of a matter from 10 kg to 20 kg (say), is due to the increase in the volume (values twice that of the matter). The increased weight of the matter from 10 kg to 20 kg is similar to the increase in the amount of matter running from 50 kg to 60 kg.
Moreover, it is important to note that the Celsius scale does not work with the heat energy in this mode. The differences of 10°C and 20°C to that of 20°C and 30°C are only 10°C. This is because temperature of 10°C exert two times heat energy, which is not exerted by a temperature of 20°C
Read more: Carnot Energy
The Modern Celsius Scale
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The Modern Celsius scale is based on the triple point of Vienna Standard Mean Ocean Water, and on the concept of the absolute zero. This implies that the modern celsius scale does not describe the boiling and melting point of water.
The differences between the formal definition and the common definition of the Celsius scale are insignificant when it is used in a practical setting. There is a difference of only 16.1 milli kelvins between the modern scale calculation of the original scale of calculation to the boiling point of water.
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Centigrade versus Celsius
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In the 19th century, thermometry and scientific communities throughout the world have used the "centigrade scale". They often recorded the temperature as "degrees" or, "degrees centigrade” when greater specificity was desired with the symbol °C.
The term "Centigrade" was used by the French and Spanish people as an angular measurement unit of 1/100 of a right angle. Terms like a gradient or centesimal degree ("gon" or "grad": 1g = 0.9°, 100g = 90°) were used when an unambiguous language was needed by then international standards bodies like the BIPM.
In order to get rid with the confusion between the unit for angular measurement and unit of temperature, in the 9th meeting of the General Conference on Weights & Measures and the Comity International des Poids et Measures, it was decided to adopt the "degree Celsius" unit for temperature, and the degree symbol (°), instead of the centesimal or gradian degree symbol (gon or g).
Read more: Kelvin Planck Statement
Differences between the Celsius Scale vs Fahrenheit Scale
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Let us discuss the key differences between the Celsius scale and the Fahrenheit Scale tabulated below:
| Comparison Factor | Celsius Scale | Fahrenheit Scale |
|---|---|---|
| Definition | The boiling point of water in the Celsius scale is 100°C and the freezing point of water is at 0°C. | The boiling point of water in the Fahrenheit scale is 212°F and the freezing point of water at 32°F. |
| Denoted By | The Celsius scale is denoted as °C (Degree C). | Fahrenheit Scale is denoted as °F (Degree F). |
| The average temperature of a human body | The average human body temperature is 37°C. | The average human body temperature is 98.6°F. |
| Divisions | The melting and boiling point of water is divided into 100 equal divisions. Each of them are represented at 1°C. | The melting and boiling point of water is divided into 180 equal divisions. Each of them are represented at 1°F. |
| Usage | It is widely used in every part of the world. | It is mostly used in the United States and few of its territories. |
Things to Remember
- Celsius scale is defined as the temperature scale based on 100° for the boiling point, and 0° for the freezing point of water
- There is a difference of only 16.1 millikelvins between the modern scale calculation and the original scale of calculation of the boiling point of water.
- In the 9th meeting of the General Conference on Weights & Measures and the Comity International des Poids et Measures, it was decided to adopt the "degree Celsius" unit for temperature, and the degree symbol to be (°), instead of the centesimal or gradian degree symbol (gon or g).
- On the Celsius scale, the boiling point of water is 100°C and the freezing point of water is at 0°C.
- The average human body temperature is 37°C.
Sample Questions
Ques: On what basis does the Celsius scale is based? (1 Mark)
Ans: The Celsius scale is based on the temperature range in which the boiling point is 100 degrees Celsius, and the freezing point is 0 degrees Celsius. The boiling point of water is the mean barometric pressure at the mean sea level.
Ques: What is the lowest temperature on the Celsius scale? (1 Mark)
Ans: The lowest Celsius temperature is -273.15 degrees Celsius.
Ques: What is the freezing and boiling point of water on the Fahrenheit scale? (1 Mark)
Ans: The freezing and boiling point of water on the Fahrenheit scale is 212 and 32 degree Fahrenheit respectively.
Ques: Is there any relation between the Celsius scale and Kelvin Scale? (1 Mark)
Ans: The temperature from the kelvin scale can be converted to the Celsius scale by subtracting 273.15 from the Kelvin temperature value.
Ques: Calculate the temperature on celsius scale whose value is half the absolute scale reading? (2 Marks)
Ans: Given: Celsius scale and absolute reading scale is C and A
According to the question, celsius scale is half of absolute reading that is
C = A/2
The relation between celsius and absolute scale is given as:
A=273+C
Now substitute the value of C
A=273+ A/2
A/2 =273
A=546
Now, substitute the value calculated in the relation between celsius and absolute scale, we get
C = A/2
C=273
So, the temperature on the celsius scale will be 273°C.
Ques: Find the ratio of the boiling point of water and melting point of water in Kelvin scale. (2 Marks)
Ans: The boiling point of water = 100°C = 373K
The melting point of water = 0°C = 273K
Ratio between the boiling point of water and melting point of water (in Kelvin) = 273K / 373K = 1.366
Ques: Convert the following temperatures to the Celsius scale-
(a) 293K
(b) 470K (2 Marks)
Ans: The relation between celsius and kelvin is given as:
t°C=TK- 273.15
(a) 293 K
Temperature in Celsius= (293−273.15)°C = 19.85°C
(b) 470 K
Temperature in Celsius= (470−273.15)°C = 196.85°C
Ques: Convert the following temperatures to the Kelvin scale.
(a) 25°C
(b) 373°C (2 Marks)
Ans: The formula for the conversion of Celcius and Kelvin is:
TK= t°C + 273.15
(a) 25°C
Temperature in Kelvin = (25+273.15) K
= 298.15 K
(b) 373°C
Temperature in Kelvin = (373+273.15) K
= 646.15 K
Ques: Write the basic difference between Celsius and Fahrenheit Scale. (3 Marks)
Ans: The difference between Celsius and Fahrenheit Scale is given below:
| Celsius Scale | Fahrenheit Scale |
|---|---|
| The boiling point of water in the Celsius scale is 100°C and the freezing point of water is at 0°C. | The boiling point of water in the Fahrenheit scale is 212°F and the freezing point of water at 32°F. |
| The Celsius scale is denoted as °C (Degree C). | Fahrenheit Scale is denoted as °F (Degree F). |
| The average human body temperature is 37°C. | The average human body temperature is 98.6°F. |
| The melting and boiling point of water is divided into 100 equal divisions. Each of them are represented at 1°C. | The melting and boiling point of water is divided into 180 equal divisions. Each of them are represented at 1°F. |
| It is widely used in every part of the world. | It is mostly used in the United States and few of its territories. |
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