Adiabatic Process
PV^γ = const — steeper than isotherm.
Key Notes
Adiabatic process: NO heat exchange with surroundings (Q = 0).
Achieved by: thermal insulation OR fast process (no time for heat to flow).
First law: ΔU = −W. If gas expands (W > 0), T DROPS. Compression heats it up.
For ideal gas: PV^γ = constant, where γ = C_p/C_v.
Equivalently: TV^(γ−1) = const, or T·P^((1−γ)/γ) = const.
Adiabatic curve on PV diagram is STEEPER than isotherm (P drops faster for same V increase).
Examples: rapid compression in a diesel engine (no time for heat loss), atmospheric air parcels rising.
Adiabatic expansion is how gas in clouds cools and condenses (rising air, lower P, lower T).
Formulas
Adiabatic condition
No heat exchange.
PV relation
γ = C_p/C_v (1.67 for monatomic, 1.4 for diatomic).
TV relation
Useful for T-V problems.
Work done by gas (adiabatic)
Direct formula for adiabatic work.
ΔU for adiabatic
Q = 0 in first law.
Important Points
Adiabatic = no heat flow. Either insulated or too fast for heat to flow.
Adiabatic expansion: gas COOLS (energy goes to work).
Adiabatic compression: gas HEATS UP (work done on gas becomes internal energy).
PV^γ vs PV: adiabatic curve drops steeper than isothermal (γ > 1).
Diesel engine: adiabatic compression heats air to ignition temperature.
Atmosphere: parcels rising cool adiabatically (~9.8°C per km dry adiabatic lapse rate).
Adiabatic Process notes from sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs, Physics Lab). Class 11 physics revision for JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT, and CUET-UG.