A teacher demonstrated the relationship between the pressure in a gas and the volume of the gas - AQA - GCSE Physics - Question 9 - 2021 - Paper 1

One control variable in the investigation could be the mass of gas in the syringe.

Using the formula for pressure, we can take the constant from the previous measurement:

1. The constant when volume was 45 cm³ was 60 kPa: $p_1 = 60 \, \text{kPa}, \ V_1 = 45 \, \text{cm}^3$ To find the pressure at volume 40 cm³, we use the equation of state for the gas (assuming ideal gas behavior): $p_1 V_1 = p_2 V_2$ Rearranging for p_2 gives us: $p_2 = \frac{p_1 \cdot V_1}{V_2}$ Substituting the values: $p_2 = \frac{60 \, \text{kPa} \cdot 45 \, \text{cm}^3}{40 \, \text{cm}^3} = 67.5 \, \text{kPa}$ Therefore, the pressure in the gas when the volume was 40 cm³ is approximately 67.5 kPa.

When the volume of gas in the syringe increased, the pressure decreased because:

1. There is more time between collisions of particles and the walls of the syringe, leading to reduced force exerted on the walls per unit area.
2. There are also less frequent collisions between the particles and the walls of the syringe.
3. This leads to a lower average force on the walls of the syringe, resulting in lower pressure.