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Thermal physics (A-level only)

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Question 4

An industrial quality-assurance test is conducted to estimate the value of absolute zero using a gas-sampling cylinder under the principles of Charles's Law.

  1. A heavy-walled cylinder with a total internal volume of V=450 cm3V = 450\text{ cm}^3V=450 cm3 is heated inside a constant-temperature steam-jacketed chamber at 98 ∘C98\ ^\circ\text{C}98 ∘C with its sampling valve open, allowing the air inside to reach thermal equilibrium with the chamber.
  2. The valve is then sealed, trapping the hot air inside.
  3. The cylinder is inverted and completely submerged into a cold ethylene glycol cooling bath maintained at −15 ∘C-15\ ^\circ\text{C}−15 ∘C.
  4. The valve is opened while submerged in the glycol, allowing liquid glycol to enter the cylinder as the trapped air cools and contracts.
  5. The depth of the cylinder is adjusted until the liquid level inside the cylinder is at the exact same height as the liquid level in the bath. The valve is then closed, trapping both the remaining air and the entered liquid inside.
  6. The cylinder is removed from the bath, and the volume of ethylene glycol that entered is measured to be 138 cm3.
a.

Explain why the depth of the cylinder must be adjusted so that the liquid levels inside and outside the cylinder are equal before closing the valve.

[2]
b.

State the volume of the trapped air when: (i) the cylinder was in the hot steam-jacketed chamber at 98 ∘C98\ ^\circ\text{C}98 ∘C, (ii) the cylinder was in the cold cooling bath at −15 ∘C-15\ ^\circ\text{C}−15 ∘C.

[2]
c.

Using the values above and Charles's Law, calculate an estimate for the value of absolute zero in ∘C^\circ\text{C}∘C.

[4]

Thermal physics (A-level only) Questions

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