Basics of Thermodynamics: First Law, Heat Transfer & Examples
Understand the fundamentals of thermodynamics — the study of heat, energy, and work. Learn the First Law of Thermodynamics, the three methods of heat transfer, and real-world applications.
What is Thermodynamics?
Thermodynamics is the branch of physics that deals with heat, temperature, energy, and the relationships between them. It explains how energy is converted from one form to another and how it flows between systems.
The **First Law of Thermodynamics** is essentially the law of conservation of energy applied to heat and work.
First Law of Thermodynamics
Energy cannot be created or destroyed — only converted from one form to another.
ΔU = Q – W
Where:
ΔU = Change in internal energy
Q = Heat added to the system
W = Work done by the system
This is the mathematical expression of energy conservation in thermodynamic processes.
Methods of Heat Transfer
1. Conduction
Transfer of heat through direct contact between particles. Occurs mainly in solids.
Example: A metal spoon getting hot in a hot soup.
2. Convection
Transfer of heat by the movement of fluids (liquids or gases).
Example: Boiling water in a pot — hot water rises, cooler water sinks.
3. Radiation
Transfer of heat through electromagnetic waves. Requires no medium.
Example: Heat from the Sun reaching Earth, or warmth from a fireplace.
Real-Life Applications
Refrigerators & Air Conditioners
They use the First Law by transferring heat from inside to outside using work (electricity).
Engines (Car, Jet, Rocket)
Heat from fuel is converted into mechanical work according to the First Law.
Human Body
Your body maintains temperature through heat transfer (sweating = evaporation, radiation from skin).
Cooking
Heat is transferred by conduction (pan), convection (boiling), and radiation (grill).
Solved Practice Problems
Problem 1: 500 J of heat is added to a system and the system does 300 J of work. What is the change in internal energy?
ΔU = Q – W = 500 – 300 = 200 J
Problem 2: Why does a metal spoon heat up faster than a wooden spoon when placed in hot soup?
Answer: Metals are good conductors of heat (conduction is faster).
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