Air escaping from a suddenly bursting tyre cools. The correct relation to use is:
- $PV=K$
- $PT^{-1}=K$
- $PV=nRT$
- $P^{\gamma-1}T^{-\gamma}=K$
Show answer and solution
Correct answer: D. $P^{\gamma-1}T^{-\gamma}=K$
1. A tyre bursting is sudden, so no appreciable heat is exchanged with the surroundings.
2. A process with no heat transfer is adiabatic, not isothermal and not isobaric.
3. The adiabatic relation between pressure and temperature is $P^{\gamma-1}T^{-\gamma}=K$.
4. Equivalently $T_1^{\gamma}P_1^{1-\gamma}=T_2^{\gamma}P_2^{1-\gamma}$ connects the two states.
5. Boyle's law holds the temperature fixed and the pressure law holds the volume fixed, so neither describes a burst; both were recorded errors.
_Source: NECTA ACSEE 2023 Physics 131/1, Question 5:Heat (Thermometers and First law of Thermodynamics)_