Heat and Temperature
Original Scanned PDF – View Notes
Temperature Scales
1. Celsius Scale
Lower fixed point: 0°C
Upper fixed point: 100°C
2. Kelvin Scale
Lower fixed point: 273 K
Upper fixed point: 373 K
3. Fahrenheit Scale
Lower fixed point: 32°F
Upper fixed point: 212°F
4. Réaumur Scale
Lower fixed point: 0°R
Upper fixed point: 80°R
Temperature Conversion Formula
The scanned notes first express the general scale relation as:
Applying the lower and upper fixed points of the Celsius, Fahrenheit, Kelvin and Réaumur scales:
Solved Temperature Numericals
Numerical 1 – Celsius and Fahrenheit Coincide
Question: At what temperature does the Celsius scale coincide with the Fahrenheit scale?
Let F = C = x.
Using:
C/100 = (F − 32)/180
x/100 = (x − 32)/180
180x = 100x − 3200
80x = −3200
x = −40
Thus the Celsius and Fahrenheit scales coincide at −40°C = −40°F.
Numerical 2 – Celsius Reading Double the Fahrenheit Reading
Question: At what temperature will the Celsius scale reading be double the Fahrenheit scale reading?
Let F = x, then C = 2x.
C/100 = (F − 32)/180
2x/100 = (x − 32)/180
360x = 100x − 3200
The source writes: x = 12.3°F
The result above is reproduced from page 2 of the supplied handwritten notes. It is kept as written rather than silently changing the source calculation.
Thermal Equilibrium
When a hot body is kept in contact with a cold body, heat flows from the hot body to the cold body until they attain the same temperature. When their temperatures become equal, the bodies are said to be in thermal equilibrium.
Zeroth Law of Thermodynamics
Verification
Consider three bodies A, B and C joined as shown. A and B are separated from each other by an insulating wall, while each is in conducting contact with C.
Let TA, TB and TC be the temperatures of A, B and C respectively.
Since A and C are in thermal equilibrium:
TA = TC … (i)
Since B and C are in thermal equilibrium:
TB = TC … (ii)
From (i) and (ii):
TA = TB
Thus, if A and B are separately in thermal equilibrium with C, then A and B are also in thermal equilibrium with each other.
Difference Between Heat and Temperature
| Heat | Temperature |
|---|---|
| It is a form of energy. | It is the degree of hotness or coldness of a body. |
| It is measured by a calorimeter. | It is measured by a thermometer. |
| Its SI unit is joule. | Its SI unit is kelvin. |
| It is a cause. | It is an effect. |
Discussion
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