First Law Of Thermodynamics Q U W — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
First Law of Thermodynamics (ΔQ = ΔU + ΔW) Applicable to closed thermodynamic systems where energy is conserved. Postulate the Conservation of Energy. Define Internal Energy (U) as a state function representing the energy stored within the system. Define Heat (Q) and Work (W) as modes of energy transfer across the system boundary. Equate net energy transfer into the system (Q - W by) to the change in stored energy (ΔU). System must be closed (no mass transfer). Sign convention must be consistent (Work done BY system is positive in this specific formulation). Confusing Work done BY the system (positive W) with Work done ON the system (negative W). Assuming Q and W are state functions (they are path functions). Thinking internal energy change ΔU is always proportional to temperature change (only true for ideal gases).