Question Constellation Sign up for free

AQA · GCSE · Physics · Higher

Fire Piston Temperature Change

Q08.3 4 marks

When the air is hot enough, a small piece of cotton wool in the piston catches fire.

The energy transferred to the air in the piston is 0.0130 J.

The mass of air in the piston is 2.60 × 10⁻⁸ kg.

specific heat capacity of air = 1.01 kJ/kg °C
change in thermal energy = mass × specific heat capacity × temperature change, ΔE=mcΔθ\Delta E=mc\Delta\theta

Calculate the temperature change of the air.

Use the Physics Equations Sheet.

Write your answer first. You can study the marking guidance whenever you need it.

Answer this question
Study the marking See what earns credit and compare it with a full-mark answer.

Marking points

  1. 1 Converts 1.01 kJ/kg °C to 1010 J/kg °C, or consistently converts the energy to kJ.
  2. 2 Uses ΔE = mcΔθ with the given mass and energy.
  3. 3 Rearranges correctly for temperature change.
  4. 4 Obtains approximately 495 °C, subject to official error-carried-forward guidance.

Full-mark answer

c=1.01 kJ kg−1 °C−1=1010 J kg−1 °C−1c=1.01\text{ kJ kg}^{-1}\,°\text{C}^{-1}=1010\text{ J kg}^{-1}\,°\text{C}^{-1}. Using ΔE=mcΔθ\Delta E=mc\Delta\theta, \(δθ=0.0130/(2.60×10^{-8}×1010)=495\,°text{C}\).

Why this answer loses marks

I substituted the specific heat capacity in kilojoules with the energy in joules.

The energy units must match before using ΔE = mcΔθ; convert one quantity consistently, then rearrange for temperature change.

Answer this question