Gases, Pressure, Flow and Fluid Physics
Gas laws, vapours, diffusion, flow, viscosity, resistance, pressure, humidity and heat transfer.
How to prepare for the current Primary FRCA MCQ
Build mechanisms first, practise calculations with units, connect equipment to failure modes and finish every SBA by choosing the single best answer to the exact lead-in.
Core concepts
Concept 1
SI units, dimensions, gas laws and proportional reasoning underpin safe anaesthetic calculations.
Exam cue: Write units at every step and estimate the expected order of magnitude.
Concept 2
Pressure, density, viscosity, radius, flow regime and resistance explain gas delivery, breathing systems and biological flow.
Exam cue: Identify whether the relationship assumes an ideal gas, laminar flow or another limiting condition.
Risk pitfalls and guardrails
Substituting values before converting units.
Guardrail: Convert units before substitution and reject an answer whose direction or order of magnitude is implausible.
Applying a laminar-flow equation unchanged to turbulent flow.
Guardrail: Do not choose an option merely because it states a true fact; choose the one that best answers the exact lead-in under the stated conditions.
Memory anchors
What is the safest calculation sequence?
State the relationship, convert units, substitute, calculate, restore units and check magnitude and direction.
What links pressure and volume at constant temperature?
For a fixed amount of ideal gas, their product remains constant.
What links gas volume and absolute temperature at constant pressure?
Volume is proportional to absolute temperature.
Why is tube radius crucial in laminar flow?
Poiseuille behaviour makes flow proportional to the fourth power of radius under its assumptions.
What promotes turbulent flow?
Higher velocity and density, larger diameter and lower viscosity increase Reynolds number.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
Boyle's law states that, at constant temperature, pressure is inversely proportional to what?
A 100 mL gas bubble at 2 atmospheres is brought to 1 atmosphere at constant temperature. What is its new volume?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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