State what is meant by the internal energy of an ideal gas.
Use the equations below to show that the average kinetic energy of a molecule in an ideal gas is directly proportional to the absolute temperature of the gas.
pV=13Nmc2‾andpV=NkT pV = \frac{1}{3}N m \overline{c^2} \quad \text{and} \quad pV = NkT pV=31Nmc2andpV=NkTIn a gas discharge experiment, the speeds of four gas molecules at a temperature of 350 K350\text{ K}350 K are measured as:
180 m s−1,240 m s−1,310 m s−1,420 m s−1 180\text{ m s}^{-1}, \quad 240\text{ m s}^{-1}, \quad 310\text{ m s}^{-1}, \quad 420\text{ m s}^{-1} 180 m s−1,240 m s−1,310 m s−1,420 m s−1Show that the root-mean-square (r.m.s.) speed of this four-particle sample is approximately 300 m s−1300\text{ m s}^{-1}300 m s−1.
Calculate the molar mass of the gas, assuming an absolute temperature of 350 K350\text{ K}350 K and an r.m.s. speed of 300 m s−1300\text{ m s}^{-1}300 m s−1.
High-intensity discharge (HID) headlight bulbs are manufactured by sealing a quartz arc chamber filled with gas at 290 K290\text{ K}290 K and low pressure.
When the headlight is switched on, the discharge arc heats the gas to a steady operating temperature of 1200 K1200\text{ K}1200 K. At this temperature, the gas pressure inside the chamber is 240 kPa240\text{ kPa}240 kPa.
Explain, in terms of energy transfers, why the temperature of the gas in the chamber does not increase beyond 1200 K1200\text{ K}1200 K.
Calculate the pressure of the gas within the chamber during its manufacture at 290 K290\text{ K}290 K.
56 exam-style questions on OCR A A Level Physics Thermal physics, covering Temperature, Solid, liquid and gas, Thermal properties of materials, and Ideal gases. Each one has a worked solution and a mark scheme showing where the marks go.