Refrigerator / Heat Pump
COP = Q_c / W — work input pulls heat from cold.
Key Notes
Refrigerator: device that EXTRACTS heat from a cold reservoir and DUMPS it to a hot reservoir, using work INPUT.
Reverse of heat engine — runs the cycle counter-clockwise.
Work IN, heat OUT to atmosphere. Q_h = W + Q_c (energy conservation).
Coefficient of Performance: COP = Q_c/W = heat extracted per unit work input.
Carnot refrigerator COP: COP_max = T_c/(T_h − T_c). Can exceed 1.
Heat pump: same machine but operated for HEATING. COP_heat = Q_h/W = 1 + COP_ref.
Real refrigerators: COP ~ 2-4 for household, 3-5 for AC. Heat pumps: 3-5 for heating.
Clausius statement (2nd law): Cannot transfer heat from cold to hot without work input.
Formulas
Refrigerator energy balance
Hot dumped = work input + cold extracted.
Coefficient of performance (refrigerator)
Higher COP = more efficient cooling per joule.
Carnot COP_ref
Maximum possible.
Heat pump COP
For HEATING applications.
Important Points
Refrigerator = REVERSED heat engine. Uses work to pump heat 'uphill'.
COP > 1 means more heat moved than work invested — common because work input ALSO becomes heat at the hot side.
Carnot COP is the upper bound: larger when reservoirs are close in T.
Heat pump for heating: gives Q_h = W + Q_c — total heating output exceeds work input, very efficient in mild climates.
Clausius statement: heat flowing from cold to hot REQUIRES work — 2nd law in disguise.
Refrigerator works because of phase changes (refrigerant evaporates, absorbs heat; condenses, releases heat).
Refrigerator / Heat Pump 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.