Flow physics: laminar flow: practice question

A Anaesthesia question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Anaesthesia · Flow physics: laminar flow

Sample item

Gas moves through a long, narrow, smooth tube at low velocity. Halving the radius at the same driving pressure reduces flow sixteen-fold, and the property of the gas that matters most is its viscosity. Which type of flow is described?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. Laminar flow

In laminar flow the gas moves in parallel layers, and flow follows the Hagen-Poiseuille relationship, proportional to the fourth power of radius and inversely proportional to viscosity and length. In turbulent flow density becomes the key property, and flow varies roughly with the square root of the pressure drop.

Option by option

  • A. Laminar flow (correct)

    Correct. Dependence on radius to the fourth power and on viscosity marks laminar flow.

  • B. Transitional flow

    Transitional flow is a mixture of the two patterns and has no single simple law.

  • C. Orifice flow

    Orifice flow through a short constriction is density dependent and not radius to the fourth power.

  • D. Turbulent flow

    Turbulent flow depends mainly on gas density, not viscosity.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Anaesthesia question

What is the answer to this Anaesthesia question?

The best answer is A, Laminar flow. In laminar flow the gas moves in parallel layers, and flow follows the Hagen-Poiseuille relationship, proportional to the fourth power of radius and inversely proportional to viscosity and length.

Why is "Transitional flow" not the answer?

Transitional flow is a mixture of the two patterns and has no single simple law.

Why is "Orifice flow" not the answer?

Orifice flow through a short constriction is density dependent and not radius to the fourth power.

Why is "Turbulent flow" not the answer?

Turbulent flow depends mainly on gas density, not viscosity.

What concept does this question test?

It tests Flow physics: laminar flow in Anaesthesia. In turbulent flow density becomes the key property, and flow varies roughly with the square root of the pressure drop.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Flow physics: laminar flow?

Make a table of each agent, its key advantage and its main side effect. Then use the flashcards and the other Anaesthesia questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.