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Working as a Physicist

Uncertainty and how uncertainties combine

  • 2 things to know
  • Papers 1, 2 and 3

Overview

Recall questions on estimating uncertainty from an analogue scale, a digital meter and repeated readings, and on adding absolute or percentage uncertainties.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Evaluation

How is the uncertainty in an analogue and in a digital reading estimated, and can readings be precise but not accurate?

Evaluation

How are uncertainties combined when quantities are added, multiplied, or raised to a power?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What does the uncertainty in a measurement tell you?

    Model answer

    It gives the interval either side of the reading within which the true value is expected to lie.

  2. 2

    How is the uncertainty in a single reading taken from an analogue scale usually estimated?

    Model answer

    It is taken as half the smallest scale division.

  3. 3

    How is the uncertainty in a reading from a digital meter usually taken?

    Model answer

    It is taken as plus or minus the last displayed digit, which is the resolution of the instrument.

  4. 4

    How is the uncertainty found from a set of repeated readings?

    Model answer

    It is taken as half the range, that is half the difference between the largest and the smallest value.

  5. 5

    How are uncertainties combined when two quantities are added or subtracted?

    Model answer

    Their absolute uncertainties are added.

  6. 6

    How are uncertainties combined when two quantities are multiplied or divided?

    Model answer

    Their percentage uncertainties are added.

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