Equipment: rotameter: 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 · Equipment: rotameter

Sample item

A rotameter on an anaesthesia machine measures gas flow using which principle?

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

The answer and the reasoning

B. A bobbin floating in a tapered tube, with flow changing from laminar to turbulent

In a rotameter the bobbin floats where the upward gas force equals its weight, in a tube that is tapered, wider at the top. At low flow the annulus is tube-like and flow is laminar, depending on viscosity, and at high flow it is orifice-like and depends on density. Each tube is calibrated for a specific gas.

Option by option

  • A. Pressure drop across a Venturi

    A Venturi is used for entrainment masks.

  • B. A bobbin floating in a tapered tube, with flow changing from laminar to turbulent (correct)

    Correct. A bobbin in a tapered tube indicates flow.

  • C. Heated wire cooling only

    Hot wire anemometers use a different method.

  • D. Ultrasonic Doppler shift

    Doppler is not used in rotameters.

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 B, A bobbin floating in a tapered tube, with flow changing from laminar to turbulent. In a rotameter the bobbin floats where the upward gas force equals its weight, in a tube that is tapered, wider at the top.

Why is "Pressure drop across a Venturi" not the answer?

A Venturi is used for entrainment masks.

Why is "Heated wire cooling only" not the answer?

Hot wire anemometers use a different method.

Why is "Ultrasonic Doppler shift" not the answer?

Doppler is not used in rotameters.

What concept does this question test?

It tests Equipment: rotameter in Anaesthesia. At low flow the annulus is tube-like and flow is laminar, depending on viscosity, and at high flow it is orifice-like and depends on density. Each tube is calibrated for a specific gas.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Equipment: rotameter?

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.