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Thermal physics (A-level only)

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Question 14
1.

In the kinetic theory of gases, we derive the equation pV=13Nm(crms)2pV = \frac{1}{3}Nm(c_{\text{rms}})^2pV=31​Nm(crms​)2 under several simplifying assumptions. State two assumptions made in this derivation, other than that the particles are identical and in continuous, rapid, random motion.

[2]
2.

Using Newton's laws of motion, explain how the microscopic collisions of gas molecules with the container walls result in a macroscopic force exerted on the walls.

[3]
3.

A high-altitude weather balloon has a volume of 0.45 m30.45\text{ m}^30.45 m3 containing helium gas at a pressure of 75 kPa75\text{ kPa}75 kPa. The mean kinetic energy of the helium atoms is 4.2×10−21 J4.2 \times 10^{-21}\text{ J}4.2×10−21 J. Calculate the amount of helium gas in the balloon in moles.

[3]
4a.

A gas cylinder is tested under isothermal conditions. A graph is plotted showing how its pressure varies with volume for a fixed mass of gas at an absolute temperature TTT. Describe how the curve of pressure against volume at temperature 1.8T1.8T1.8T compares to the original curve plotted at temperature TTT.

[2]
4b.

A point on the original curve has coordinates (0.015 m3,240 kPa)(0.015\text{ m}^3, 240\text{ kPa})(0.015 m3,240 kPa). Calculate the pressure of the gas at this same volume of 0.015 m30.015\text{ m}^30.015 m3 when the temperature is raised to 1.8T1.8T1.8T.

[2]

Thermal physics (A-level only) Questions

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