Temperature & Scales of Temperature
Learn how temperature is measured, understood, and compared across different scales.
Introduction
In mechanics, the three fundamental quantities are mass, length, and time.
To study thermal phenomena, we introduce another quantity: temperature.
Together with volume, pressure, and number of molecules, it defines the state of matter.
The equation of state relates these physical quantities, often explained by the Kinetic Molecular Model of an Ideal Gas.
Temperature
Definition: Temperature is the measure of the average kinetic energy of molecules in a body.
Measurement
Thermometers use thermal equilibrium:
- Heat flows from hot to cold when in contact.
- It stops once both reach the same temperature (equilibrium).
Scales of Temperature
Celsius (°C)
- Introduced by Anders Celsius.
- 0 °C → Freezing point, 100 °C → Boiling point.
Fahrenheit (°F)
- Introduced by Daniel Fahrenheit.
- 32 °F → Freezing point, 212 °F → Boiling point.
Kelvin (K)
- SI unit of temperature.
- Freezing = 273 K, Boiling = 373 K.
- Absolute zero (0 K) is the lowest possible temperature.
Formula: T(K) = T(°C) + 273
Conversion Between Scales
(T - LFP)/(BP - LFP) = (T' - LFP')/(BP' - LFP')
LFP = Lower Fixed Point, BP = Boiling Point.
Common Conversions
- C → K: K = °C + 273
- C → F: °F = (9/5 × °C) + 32
- F → C: °C = (5/9) × (°F - 32)
Human Body Temperature
36.9 °C = 310 K ≈ 98.4 °F
Comparison Table
| Scale | Freezing | Boiling | Absolute Zero | Inventor |
|---|---|---|---|---|
| Celsius | 0 °C | 100 °C | -273.15 °C | Anders Celsius |
| Fahrenheit | 32 °F | 212 °F | -459.67 °F | Daniel Fahrenheit |
| Kelvin | 273 K | 373 K | 0 K | Lord Kelvin |
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