What is the First Law of Thermodynamics?

ΔU = Q − W. The change in internal energy equals heat added to the system minus work done by the system. It is essentially conservation of energy.

Why is Carnot engine maximum efficient?

The Carnot engine operates on a reversible cycle — all processes are quasi-static and no energy is wasted to friction or irreversibility. This gives the theoretical upper limit η = 1 − T₂/T₁.

What happens in an adiabatic process?

No heat exchange (Q = 0), so ΔU = −W. The gas cools if it expands and heats up if compressed. Relation: PVγ = constant.

Laws of Thermodynamics

Thermodynamics • Class 11 Physics • NCERT • CBSE

First Law of Thermodynamics: ΔU = Q − W (energy is conserved). Second Law: Heat cannot spontaneously flow from cold to hot. Efficiency of heat engine: η = 1 − T₂/T₁. Carnot engine gives maximum efficiency between two temperatures.

Key Formulas

ΔU = Q − W (First Law)
η = 1 − T₂/T₁ (Carnot efficiency)
W = nRT ln(V₂/V₁) (Isothermal work)
PVγ = constant (Adiabatic process)
COP = T₂/(T₁ − T₂) (Refrigerator)

Frequently Asked Questions

What is the First Law of Thermodynamics?: ΔU = Q − W. The change in internal energy equals heat added to the system minus work done by the system. It is essentially conservation of energy.
Why is Carnot engine maximum efficient?: The Carnot engine operates on a reversible cycle — all processes are quasi-static and no energy is wasted to friction or irreversibility. This gives the theoretical upper limit η = 1 − T₂/T₁.
What happens in an adiabatic process?: No heat exchange (Q = 0), so ΔU = −W. The gas cools if it expands and heats up if compressed. Relation: PVγ = constant.

Study With GyanAI

GyanAI's AI tutor can answer any question about this topic instantly. Try GyanAI free for step-by-step NCERT solutions aligned with the CBSE curriculum.