A student investigated how the pressure of a gas depends on its temperature - AQA - GCSE Physics Combined Science - Question 4 - 2022 - Paper 1

To find the mean pressure, first calculate the average of the four readings:

$ext{Mean Pressure} = \frac{0.115 + 0.120 + 0.121 + 0.116}{4} = 0.118 \text{ MPa}$

Next, calculate the range and uncertainty. The range of the readings is:

$\text{Range} = 0.121 - 0.115 = 0.006 \text{ MPa}$

The uncertainty is then half the range:

$\text{Uncertainty} = \frac{0.006}{2} = 0.003 \text{ MPa}$

The relationship between temperature and pressure is linear within the range of the measurements. As temperature increases, the average kinetic energy of the gas particles also increases, leading to more frequent and forceful collisions with the walls of the container, which in turn results in an increase in pressure.

When the water in the pressure cooker begins to boil, several changes occur:

1. The amount of steam produced increases, leading to a greater number of gas particles in the confined space.
2. The temperature of the steam rises above 100 °C because the pressure increases, which raises the boiling point of the water.
3. As the number of particles and their average kinetic energy increase, this causes more collisions with the walls of the pressure cooker, thus increasing the pressure.

When steam is released from the pressure cooker through the safety valve, the pressure decreases. As a result, the steam expands as it enters the lower pressure environment of the atmosphere. This expansion increases the volume of steam as it cools and loses energy, leading to a decrease in density:

$\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

Since the mass remains constant and the volume increases, the overall density of the steam decreases.