OCR · A-Level · Physics

    Course version: H556 · Version from Sept 2015

    (e) use of calipers and micrometers for small distances, using digital or…

    Full specification wording

    Practical skills: (e) use of calipers and micrometers for small distances, using digital or vernier scales

    This skill involves using calipers and micrometers to measure small distances accurately.

    Checked against the OCR H556 specification (opens in a new tab) on .

    • Point 5 of 11
    • 3 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    This skill involves using calipers and micrometers to measure small distances accurately. Vernier calipers measure internal, external and depth dimensions, typically to 0.1 mm or 0.05 mm. Micrometers measure external dimensions to 0.01 mm. Both may have digital or vernier scales. When using vernier calipers, close the jaws to check for zero error, then place the object between the jaws and read the main scale and vernier scale. For a micrometer, use the ratchet to avoid over-tightening, and read the sleeve and thimble scales. For example, to measure the diameter of a wire, use a micrometer and record the reading in mm. The skill is assessed in practical tasks where you must select the appropriate instrument and read it correctly.

    What earns the marks

    • Select vernier calipers for internal, external or depth measurements and a micrometer for external diameters.
    • Check for zero error before taking measurements and apply a correction if necessary.
    • Read the main scale and vernier or thimble scale correctly, combining them to give the final value.
    • Use the ratchet on a micrometer to apply consistent pressure and avoid compressing the object.
    • Record measurements with the correct unit and an appropriate number of decimal places.

    Common mistakes and how to put them right

    • Forgetting to check for zero error.

      Put it right: Close the instrument and note any offset, then subtract it from readings.

    • Over-tightening a micrometer, which can deform the object or damage the instrument.

      Put it right: Use the ratchet until it clicks.

    • Misreading the vernier scale by not identifying the coinciding line correctly.

      Put it right: Find the line on the vernier that aligns exactly with a main scale mark.

    • Using calipers to measure a curved surface without ensuring the jaws are perpendicular.

      Put it right: Position the object so the jaws make full contact.

    Exam tips

    • State the instrument and its resolution, for example 'micrometer, resolution 0.01 mm'.
    • When describing a reading, explain how the main and vernier scales are combined.
    • Practise reading diagrams of vernier scales to avoid errors in identifying the coinciding line.

    Try the lesson

    The start of the Practical skills: (e) use of calipers and micrometers for small distances, using digital or vernier scales lesson, made from checked teaching notes for this specification point.

    Listen

    This skill involves using calipers and micrometers to measure small distances accurately. Vernier calipers measure internal, external and depth dimensions, typically to 0.1 mm or 0.05 mm. Micrometers measure external dimensions to 0.01 mm. Both may have digital or vernier scales. When using vernier calipers, close the jaws to check for zero error, then place the object between the jaws and read the main scale and vernier scale. For a micrometer, use the ratchet to avoid over-tightening, and read the sleeve and thimble scales. For example, to measure the diameter of a wire, use a micrometer and record the reading in mm. The skill is assessed in practical tasks where you must select the appropriate instrument and read it correctly. A strong answer earns marks for these points. Select vernier calipers for internal, external or depth measurements and a micrometer for external diameters. Check for zero error before taking measurements and apply a correction if necessary. Read the main scale and vernier or thimble scale correctly, combining them to give the final value. Use the ratchet on a micrometer to apply consistent pressure and avoid compressing the object. A common slip: Forgetting to check for zero error. Instead, close the instrument and note any offset, then subtract it from readings. Exam tip: State the instrument and its resolution, for example 'micrometer, resolution 0.01 mm'.

    See it

    A top-down flowchart. The first node, Select instrument, branches into two paths. The left path is Vernier calipers: internal, external or depth, which leads to Close jaws to check for zero error, then Place object between jaws, then Read main scale and vernier scale. The right path is Micrometer: external diameters, which leads to Use ratchet to avoid over-tightening, then Read sleeve and thimble scales. Both reading nodes join at Combine scales for final value, which leads to Record with correct unit and decimal places.
    It shows how to choose between vernier calipers and a micrometer and the steps for checking zero error, taking a reading and recording it.

    Key words

    Say what each word means before you turn the card.

    Vernier calipers

    Try answering aloud or in your head before turning the card.

    Micrometer

    Try answering aloud or in your head before turning the card.

    Ratchet

    Try answering aloud or in your head before turning the card.

    See every definition
    Vernier calipers
    An instrument used to measure internal, external and depth dimensions, typically to 0.1 mm or 0.05 mm.
    Micrometer
    An instrument used to measure external dimensions to 0.01 mm, read using the sleeve and thimble scales.
    Ratchet
    A part of the micrometer used to apply consistent pressure and avoid over-tightening, compressing the object or damaging the instrument.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-down flowchart. The first node, Select instrument, branches into two paths. The left path is Vernier calipers: internal, external or depth, which leads to Close jaws to check for zero error, then Place object between jaws, then Read main scale and vernier scale. The right path is Micrometer: external diameters, which leads to Use ratchet to avoid over-tightening, then Read sleeve and thimble scales. Both reading nodes join at Combine scales for final value, which leads to Record with correct unit and decimal places.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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