Edexcel IGCSE Physics 5.21 Pressure-temperature relationship

Practise calculating pressure or temperature for a fixed gas at constant volume, converting Celsius data to kelvin before substitution.

Exam points

convert °C to K before applying p1/T1 = p2/T2 for a fixed mass of gas
rearrange pressure-temperature equations to find p in Pa or kPa, or final °C
explain why a pressure-°C graph can be linear without passing through the origin

[Maximum number: 4]

The diagram shows a manometer, a device used for measuring differences in pressure.

Figure for Question 5.21 Pressure-temperature relationship question 1 — Edexcel IGCSE Physics

The temperature and pressure of the trapped gas increase when it is warmed.

The pressure of the trapped gas in the manometer is $9.95 \times 10^{4} \mathrm{~Pa}$ and the temperature is $16^{\circ} \mathrm{C}$ .

Calculate the new pressure of the trapped gas if the temperature increases to $32^{\circ} \mathrm{C}$ .
[assume volume of the trapped gas remains constant]
new pressure = Pa

Marking points:
- conversion of temperatures to kelvin
- substitution
- rearrangement
- evaluation

Example:
$T_1=289\ \mathrm{K},\qquad T_2=305\ \mathrm{K}$ $\frac{9.95\times10^{4}}{289}=\frac{p_2}{305}$ $p_2=\frac{9.95\times10^{4}\times305}{289}$ $p_2=1.1\times10^{5}\ \mathrm{Pa}$

Marking guidance:
- not converting to kelvin giving $199000\ \mathrm{Pa}$ gains 2 marks maximum

Accept:
- $1.05\times10^{5}\ \mathrm{Pa}$
- $105008.65\ldots\ \mathrm{Pa}$

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5.21 Pressure-temperature relationship question 1