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FCPS Part 1 Physics MCQs
Physics questions test the principles behind equipment and monitoring: gas laws, flow, humidity, pressure measurement, electrical safety and the physics of anaesthetic machines.
Below are 5 free single-best-answer questions drawn from the most frequently examined physics concepts, each with the answer and a rationale for every option. The full bank has 38 physics concepts, each asked several different ways.
Free physics questions
Question 1
Fully charged E oxygen cylinder (about 660 L) delivering 6 L/min lasts approximately:
- A. 110 min
- B. 30 min
- C. 60 min
- D. 90 min
- E. 130 min
Show answer
Answer: A. 110 min
Duration equals contents divided by flow. A full E cylinder holds about 660 L, and 660 ÷ 6 = 110 min. Oxygen is a gas, so cylinder pressure falls in proportion to contents.
Why not the others: 30 min: far too short. 60 min: assumes 360 L. 90 min: assumes 540 L. 130 min: would need about 780 L.
High-yield: Minutes = litres ÷ flow; ignore the cylinder's stated mass.
Question 2
Pulse oximetry estimating SpO₂ from red and infrared absorption rests on which law?
- A. Beer-Lambert law
- B. Boyle's law
- C. Charles's law
- D. Fick's law
- E. Henry's law
Show answer
Answer: A. Beer-Lambert law
Oxygenated and reduced haemoglobin absorb red and infrared light differently. The Beer-Lambert law relates absorbance to concentration and path length, and a microprocessor derives SpO₂ from the red to infrared ratio.
Why not the others: Boyle's law: pressure inversely related to volume at constant temperature. Fick's law: diffusion across a membrane. Henry's law: dissolved gas proportional to partial pressure. Charles's law: volume proportional to temperature. Dalton's law: partial pressures add.
High-yield: Pulse oximetry, spectrophotometry and capnography all use the Beer-Lambert law.
Question 3
A fixed mass of gas expands when heated while pressure is held constant. Law:
- A. Dalton's law
- B. Charles' law
- C. Boyle's law
- D. Graham's law
- E. Henry's law
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Answer: B. Charles' law
For a fixed mass of gas at constant pressure, volume is directly proportional to absolute temperature (V ∝ T, in kelvin).
Why not the others: Boyle's law: pressure and volume at constant temperature. Dalton's law: total pressure is the sum of partial pressures. Henry's law: dissolved gas proportional to partial pressure. Graham's law: diffusion rate and density.
High-yield: Charles holds pressure constant; Boyle holds temperature constant; always use kelvin.
Question 4
Total pressure of a gas mixture equals the sum of each component's individual pressure. This is:
- A. Dalton's law
- B. Boyle's law
- C. Graham's law
- D. Fick's law
- E. Henry's law
Show answer
Answer: A. Dalton's law
In a gas mixture each gas exerts the pressure it would alone, and the partial pressures add to the total. Dry air at 760 mmHg gives PO2 of 160 mmHg; humidified tracheal gas gives about 150 mmHg.
Why not the others: Henry's law: dissolved amount proportional to partial pressure. Boyle's law: pressure and volume at constant temperature. Fick's law: diffusion rate. Graham's law: diffusion inversely related to the square root of molecular weight.
High-yield: Dalton = divide the total pressure between the gases present.
Question 5
Instrument used to measure humidity of air or anaesthetic gas:
- A. Manometer
- B. Hygrometer
- C. Sphygmomanometer
- D. Heliometer
- E. Thermometer
Show answer
Answer: B. Hygrometer
A hygrometer measures humidity, the water vapour content of a gas. Hair, wet-and-dry bulb and Regnault's types are examples.
Why not the others: Manometer: pressure. Sphygmomanometer: arterial blood pressure. Thermometer: temperature. Heliometer: a red herring. Anemometer: wind speed.
High-yield: Hygro- = moisture; manometer = pressure.
Keep going with physics
Anaesgen brings every concept back on a spaced-repetition schedule timed to your exam date, as a different question each time, with full mock papers for Paper 1 and 2.
Get full access Try the 5 sample questionsHigh-yield physics one-liners
The most-tested physics concepts, as a clue and the answer it points to:
- Full E cylinder 660 L ÷ 6 L/min → 110 min.
- Pulse oximetry, spectrophotometry, infrared capnography → Beer-Lambert law.
- Constant pressure, V proportional to absolute temperature → Charles' law.
- Mixture, total = sum of partials, PO2 = 0.21 × pressure → Dalton's law.
- Humidity measurement; hair, wet-and-dry bulb, Regnault → hygrometer.
- Thermodilution cardiac output, saturated vapour pressure → temperature.
- Infrared ear thermometer, non-contact, junctions in series → thermopile.
- Oxygen cannot be liquefied above its critical temperature → −118°C.
- Full E-cylinder 600-660 L ÷ 5 L/min → about 2 hours.
- Water vapour mass per unit volume (mg/L, g/m³) → absolute humidity.
- Gas pocket expands as pressure falls; cylinder volume × pressure → Boyle's law.
- O2 supply pressure falls → fail-safe valve cuts off N2O.
- Heavier gas, same T and P → higher density → more turbulent resistance.
- No contact, cross-infection risk, radiated heat → infrared thermometer.
- Laminar flow, Hagen–Poiseuille, high haematocrit → viscosity.
- O2 supply pressure loss, not FiO2 or flow → fail-safe valve.
- Boyle's law, constant temperature → pressure inversely proportional to volume.
- SVP depends on agent and liquid temperature only → rises with liquid temperature.
- Orifice, turbulent flow → square root of pressure difference.
- Graham's law, light gases diffuse faster → rate ∝ 1/√MW.
Other FCPS Part 1 subjects
AnatomyPharmacologyPathologyBiochemistry & GeneticsCardiovascularNeurophysiologyMicrobiologyHaematologyGeneral PhysiologyImmunologyEndocrineRespiratoryEmbryologyObstetrics & GynaeRenal & Acid-BaseHistologyGI & LiverBiostatistics
New to the exam? Read the FCPS Part 1 exam guide: dates, format and a 12-week study plan.