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First Law of Thermodynamics Explained

📑 10 slides 👁 45 views 📅 1/24/2026
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Introduction to Thermodynamics

Thermodynamics studies energy transfer in systems.

Introduction to Thermodynamics
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The 1st Law Formula

  • ΔU = Q - W represents energy conservation.
  • ΔU: Change in internal energy of the system.
  • Q: Heat added to the system (positive if absorbed).
  • W: Work done by the system (positive if done on surroundings).
The 1st Law Formula
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Understanding Internal Energy

  • Internal energy (U) is the total energy of a system.
  • Includes kinetic and potential energy of molecules.
  • Changes with heat transfer or work done.
Understanding Internal Energy
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Heat Transfer (Q)

  • Heat is energy transferred due to temperature difference.
  • Measured in joules (J) or calories (cal).
  • Positive Q: System gains heat (endothermic).
Heat Transfer (Q)
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Work Done (W)

  • Work is energy transferred by mechanical means.
  • Examples: Gas expansion, piston movement.
  • Positive W: System does work on surroundings.
Work Done (W)
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Practical Applications

  • Used in engines, refrigerators, and power plants.
  • Explains why perpetual motion machines are impossible.
  • Essential for understanding heat pumps.
Practical Applications
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Example: Car Engine

  • Fuel combustion adds heat (Q) to the system.
  • Piston movement does work (W) on surroundings.
  • ΔU decreases as energy converts to motion.
Example: Car Engine
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Example: Refrigerator

  • Work (W) is done to remove heat (Q) from inside.
  • ΔU remains constant in a cyclic process.
  • Energy is conserved but redistributed.
Example: Refrigerator
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Common Misconceptions

  • Energy is not lost, just transformed or transferred.
  • Isolated systems have constant total energy.
  • Work and heat are not properties of a system.
Common Misconceptions
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Conclusion & Summary

  • 1st Law: Energy is conserved in all processes.
  • ΔU = Q - W is the fundamental energy balance.
  • Applies universally in physics and engineering.
Conclusion & Summary
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