Physics 9702 · AS & A Level · Thermal equilibrium

Thermal equilibrium — practice question

Fig. 3.1 depicts a thermometer known as a constant volume gas thermometer. It is used to find the thermodynamic temperature $T$ of the gas in the glass bulb. The bulb is placed in the surroundings whose temperature is to be measured. The movable glass tube is then adjusted until the liquid level on the left-hand side is level with the reference line X on the fixed glass tube. Reference line Y is marked on the side of the movable glass tube. Because of the gas pressure in the glass bulb, the liquid at Y stands above the level at X. The height difference $\Delta h$ between the liquid levels at X and Y is then read from the scale. The thermodynamic temperature $T$ of the gas is directly proportional to the gas pressure. This pressure is directly proportional to $\Delta h$.
(a)[2]

State what is meant when two objects are in thermal equilibrium.

(b(i))[1]

The value of $\Delta h$ can be used to work out the pressure of the gas. To do this, gravitational field strength is used together with one property of the liquid. State the property of the liquid used in the pressure calculation.

(b(ii))[2]

Before $\Delta h$ is measured, the glass bulb must come to thermal equilibrium with the environment whose temperature is being measured. State two disadvantages of using a constant volume gas thermometer to measure temperature.

(b(iii))[1]

Suggest one situation in which a constant volume gas thermometer would be a suitable thermometer choice for measuring temperature.

(b(iv))[3]

Level X lines up with $2.31\,\text{cm}$ on the scale. When the temperature is $0\,^{\circ}\text{C}$, level Y lines up with $8.69\,\text{cm}$. When the temperature is $\theta$, level Y lines up with $7.83\,\text{cm}$ on the scale. Determine a value of $\theta$ in $^{\circ}\text{C}$.

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