Boyle's Law
PV = const at fixed T.
Key Notes
Boyle's law: at constant temperature, pressure × volume = constant. PV = const.
Equivalently: P₁V₁ = P₂V₂ for an ideal gas at constant T.
Inverse proportionality between P and V.
On PV diagram: hyperbola (also an isotherm).
Experimentally verified by Robert Boyle (1662) using mercury and air in a J-tube.
Microscopically: smaller V ⇒ same molecules hit walls more often ⇒ higher pressure.
Real gases deviate at high P (intermolecular forces, molecular size).
Special case of ideal gas law (PV = nRT) at constant n and T.
Formulas
Boyle's law
P ∝ 1/V at fixed T and n.
Two-state form
Same gas, same T ⇒ PV invariant.
Connection to ideal gas law
Boyle's law follows by fixing T and n.
Important Points
PV = const at FIXED T. If T changes, both can change.
Doubling P halves V (or vice versa).
Air in a sealed syringe: compress it, pressure rises predictably.
Microscopic reason: smaller V ⇒ same number of molecules ⇒ more frequent collisions ⇒ higher P.
Real gases at high P: deviation due to molecular size and attractions (van der Waals corrections).
Used in diving (Boyle's law explains why divers must equalize ear pressure during descent).
Boyle's Law 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.