Explain how a student could estimate the volume of a human lung, giving a reasonable final value with an appropriate order of magnitude.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
A student could estimate the volume of a human lung by measuring the tidal volume – the amount of air exhaled in a normal breath.
1. Invert a graduated cylinder or a water‑filled container and have the student breathe into it. The rise in water level gives the tidal volume.
2. Repeat the measurement several times (e.g. 5–10 breaths) and calculate the average to minimise experimental error.
3. Recognise that the total lung capacity is about 5–6 times the tidal volume, or use a forced full breath to obtain a larger value.
4. Multiply the average tidal volume by 5–6 to give a total lung volume of roughly 3–6 L (3000–6000 cm³ or 0.003–0.006 m³).
1. Invert a graduated cylinder or a water‑filled container and have the student breathe into it. The rise in water level gives the tidal volume.
2. Repeat the measurement several times (e.g. 5–10 breaths) and calculate the average to minimise experimental error.
3. Recognise that the total lung capacity is about 5–6 times the tidal volume, or use a forced full breath to obtain a larger value.
4. Multiply the average tidal volume by 5–6 to give a total lung volume of roughly 3–6 L (3000–6000 cm³ or 0.003–0.006 m³).
Examiner tips
- Use the word ‘average’ to show you understand uncertainty; include units in the final answer; mention that total lung capacity is larger than a single tidal breath; give a realistic range (3–6 L).
Common mistakes
- Failing to average multiple breaths, leading to a large error; giving the tidal volume as the total lung volume; omitting units or using the wrong unit (e.g. m³ instead of L).
Mark scheme (5 marks)
- Recognise that the volume of air breathed out in one breath (tidal volume) can be measured or estimated
- Describes a practical method — e.g. breathing into an inverted water-filled container or measuring how much a balloon expands
- States that multiple readings (e.g. several breaths) should be taken and an average calculated to reduce uncertainty
- Recognises that the lung volume is larger than a single tidal breath — total capacity is approximately 5–6 times a resting tidal breath, or uses a forced full breath
- States a reasonable final value for total lung volume in appropriate units — approximately 3–6 litres (3000–6000 cm³ / 0.003–0.006 m³)
Key terms in this question
Related
- All AQA A-Level Physics (7408) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Estimation of Physical Quantities questions
- A student wants to estimate the power output of a person walking up a flight of …
- A student wants to estimate the gravitational potential energy stored in a full …
- A student wants to estimate the kinetic energy of a cyclist travelling along a f…
- Explain how a student could estimate the speed of a car travelling along a road,…
- A student wants to estimate the time it takes for a human heart to beat once. Ex…
- A student is asked to estimate the density of a human body. Explain how the stud…