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Practical Skills and Data Analysis

Choosing and using measuring instruments

  • 3 things to know
  • Units AS 3 and A2 3

Overview

Recall questions on the resolution and proper use of the metre rule, the micrometer screw gauge, the vernier caliper, the balance, the stopwatch, the thermometer, the multimeter and the protractor, reading a meniscus, zero error and the ratchet, parallax on an analogue scale, and choosing an instrument so the reading fills its range.

What you need to know

Answer each one before you reveal it.

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Key term

State the resolution of a metre rule and explain why the uncertainty in a measured length is usually taken as twice that value.

Key term

What precautions are needed when a thermometer or a temperature sensor is used in a liquid?

Key term

How is a multimeter connected when used to measure resistance, potential difference and current?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Which instruments are used to measure mass, and how do they differ in what they respond to?

    Model answer

    A top-pan balance measures the downward force on the pan and is calibrated to display a mass in grams or kilograms for the local gravitational field strength, whereas a spring balance stretches under the weight of the object, so its scale depends directly on the local gravitational field strength.

  2. 2

    What is a micrometer screw gauge used for, and what is its resolution?

    Model answer

    It is used to measure small lengths such as the diameter of a wire or the thickness of a sheet, typically up to 25 mm, and its resolution is 0.01 mm.

  3. 3

    What is a vernier caliper used for, and what is its typical resolution?

    Model answer

    It measures lengths of the order of a few centimetres, including external and internal diameters and the depth of a hole, with a typical resolution of 0.1 mm or better.

  4. 4

    State the resolution of a metre rule and explain why the uncertainty in a measured length is usually taken as twice that value.

    Model answer

    The resolution is 1 mm, but a length is found from the difference between two readings, one at each end, so each carries its own reading uncertainty and the uncertainty in the difference is about 2 mm.

  5. 5

    Which length-measuring instrument would you choose for a wire of diameter about 0.4 mm, and why not the others?

    Model answer

    A micrometer screw gauge is needed, because its 0.01 mm resolution gives an uncertainty of only a few per cent on 0.4 mm, whereas a rule reading to 1 mm could not resolve the diameter at all.

  6. 6

    How should the volume of a liquid be read from a graduated cylinder?

    Model answer

    Stand the cylinder on a level surface and read the scale with the eye at the same height as the liquid surface, taking the reading at the bottom of the meniscus for water, so that parallax does not distort the value.

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