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Experimental Techniques

Physics measurements: oscillations, resistivity, lenses and critical angle

  • 3 things to know
  • AS 1

Overview

Timing pendulum oscillations with a fiducial marker, measuring resistivity with a micrometer, finding focal length with the lens formula, and measuring the critical angle and refractive index.

What you need to know

Answer each one before you reveal it.

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Key term

How is the periodic time of an oscillating pendulum measured?

Key term

Why is the time for many oscillations measured rather than one?

Key term

A pendulum makes 20 oscillations in 32.0 s. What is its period?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    How is the periodic time of an oscillating pendulum measured?

    Model answer

    The time for a set number of complete oscillations, such as 20, is measured with a stopwatch. The total is divided by the number of oscillations.

  2. 2

    Why is the time for many oscillations measured rather than one?

    Model answer

    A timing over many oscillations reduces the effect of human reaction time on the result. The percentage uncertainty becomes smaller.

  3. 3

    A pendulum makes 20 oscillations in 32.0 s. What is its period?

    Model answer

    The period is 1.60 s. The working is 32.0 ÷ 20 = 1.60 s.

  4. 4

    Why is a fiducial marker used when timing a pendulum?

    Model answer

    A fixed marker at the centre of the swing gives a clear point to start and stop timing. Timing at the fastest point is more precise.

  5. 5

    What is resistivity?

    Model answer

    Resistivity is a property of a material that shows how strongly it opposes electric current. Resistivity is measured in ohm metres.

  6. 6

    How is the resistivity of a metal wire determined?

    Model answer

    The resistance of different lengths of wire is measured, and the wire's diameter is measured with a micrometer. Resistivity equals the gradient of resistance against length multiplied by the cross-sectional area.

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