Physics
Heat and Temperature
More Articles
- Heat And Temperature
- Unit and Dimension
- Motion in Daily Life
- Work, Energy and Power
- Gravitation and Gravity
- Pressure in Liquids and Atmosphere
- Floatation in Liquids
- Surface Tension Made Simple
- Simple Harmonic Motion
- From Terminal Velocity to Elasticity
- Waves and Sound
- Thermal Expansion & Heat Transfer
- Latent Heat & Thermodynamics
- Speed of Light & Refractive Index
- Laws of Reflection & Refraction
- Power of a Lens
- Human Eye Vision Defects
- What Is Electric Charge?
- What Is Electric Current?
- Key Concepts in Magnetism
- Nuclear & Atomic Physics
- The Basics of Electronics
- Scientific Instruments & Their Uses
- Famous Inventions and Discoveries
- SI Units and Conversion Factors
Heat and Temperature
Heat
Heat is that form of energy that flows from one body to another due to the difference in temperature between them.
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The amount of heat contained in a body depends upon the mass of the body.
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If work performed is W and heat produced is H, then W = JH, where J is a constant called the Mechanical Equivalent of Heat.
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Its value is 4.186 joules/calorie, meaning that if 4.186 joules of work are performed, 1 calorie of heat is consumed.
Units of Heat
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C.G.S. unit: calorie = amount of heat required to raise the temperature of 1 g of pure water by 1°C.
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International calorie: heat required to raise 1 g of water from 14.5°C to 15.5°C.
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F.P.S. unit: B.Th.U (British Thermal Unit) = heat required to raise 1 pound of water by 1°F.
Relations Between Different Units
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1 B.Th.U = 252 calories
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1 calorie = 4.186 joules
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1 Therm = 10⁵ B.Th.U
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1 pound calorie = 453.6 calorie
Temperature
Temperature is the physical cause that decides the direction of flow of heat.
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Heat flows from a body at a higher temperature to a body at a lower temperature.
Measurement of Temperature
Thermometer
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A device that measures the temperature of a body is called a thermometer.
Scales of Temperature Measurement
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Two fixed points:
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Freezing point of water (Lower Fixed Point, LFP)
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Boiling point of water (Upper Fixed Point, UFP)
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Scale |
LFP |
UFP |
Number of Fundamental Intervals |
|---|---|---|---|
|
Celsius |
0°C |
100°C |
100 |
|
Fahrenheit |
32°F |
212°F |
180 |
|
Réaumur |
0°R |
80°R |
80 |
|
Kelvin |
273.15K |
373.15K |
100 |
|
Rankine |
492°Ra |
672°Ra |
180 |
Absolute Zero
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Celsius: -273.15°C
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Fahrenheit: -459.6°F
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Rankine: -218.4°R
Relations Between Temperature Scales
(C + 0)/100 = (F - 32)/180 = (R + 0)/80 = (K - 273)/100 = (Ra - 492)/180
Conversion Scale
ΔC/5 = ΔF/9 = ΔR/4 = ΔK/5 = ΔRd/9
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Celsius was initially known as centigrade. The
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Kelvin scale does not use the degree symbol
Range of Thermometers
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Mercury thermometer: -30°C to 350°C
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Alcohol thermometer: F.P. of alcohol -115°C
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Constant volume gas thermometer: -200°C to 500°C (with H₂), below -200°C to -268°C (with He), above 1000°C to 1600°C (with N₂ and glazed porcelain bulb)
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Platinum resistance thermometer: -200°C to 1200°C
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Thermocouple thermometer: -200°C to 1600°C
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Total Radiation Pyrometer: Measures the temperature of glowing bodies based on radiation; cannot measure below 800°C
Specific Heat Capacity
The specific heat capacity of a material is the heat required to raise the temperature of a unit mass by 1°C.
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SI unit: Joule/kg·K
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One calorie raises 1 g of water by 1°C (4200 J/kg·K)
Specific Heat Capacities of Materials
Material |
Specific Heat (J/kg·K) |
|---|---|
|
Water |
4200 |
|
Ice |
2100 |
|
Iron |
460 |
|
K. Oil |
210 |
|
Mercury |
140 |
|
Lead |
130 |
Specific Heat of Gases
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Depends on the conditions of heating
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Two significant types:
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Constant volume (sᵥ)
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Constant pressure (sₚ)
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Molar Heat Capacity
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Heat required to raise 1 mole of gas by 1°C:
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Cᵥ: at constant volume
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Cₚ: at constant pressure
-
Relations
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Adiabatic exponent γ depends on the atomicity of the gas.
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Cₚ / Cᵥ = sₚ / sᵥ = γ
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Cₚ = M * sₚ, Cᵥ = M * sᵥ (M = molar mass of gas)
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Cₚ - Cᵥ = R in SI units
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sₚ - sᵥ = R / M in SI units
Final Thoughts
Heat is energy that flows from a hotter body to a cooler one, depending on the body’s mass. The mechanical equivalent of heat shows 4.186 joules of work produce 1 calorie.
Heat is measured in calories, BTU, and joules, and thermometers track temperature on scales like Celsius, Fahrenheit, and Kelvin, with absolute zero as the lowest point. Specific heat capacity tells how much heat is needed to raise a substance’s temperature, with water at 4200 J/kg·K. For gases, heat capacity varies at constant volume or pressure, and molar heat capacity is per mole.
Understanding heat and temperature explains everyday phenomena, from cooking and climate to industrial processes.
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