Using Practical Equipment & Materials (OCR A Level Physics)

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Katie M

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Using Practical Equipment & Materials

  • Choosing the right equipment and knowing how to use it for a physics experiment is crucial
  • A list of common apparatus is shown below:

Apparatus Table, downloadable AS & A Level Physics revision notes

Measuring Instruments, downloadable AS & A Level Physics revision notes

A selection of apparatus commonly used in physics experiments

  • When using measuring instruments such as those listed above, it is important to be aware of what each division on a scale represents
    • This is known as the resolution

  • The resolution is the smallest change in the physical quantity being measured that results in a change in the reading given by the measuring instrument
  • The smaller the change that can be measured by the instrument, the greater the degree of resolution
  • For example, a standard mercury thermometer has a resolution of 1°C whereas a typical digital thermometer will have a resolution of 0.1°C
    • The digital thermometer has a higher resolution than the mercury thermometer

Using Practical Apparatus & Techniques

  • When planning and implementing a practical investigation, it is crucial to decide which apparatus is the most suitable for the intended purpose

Worked example

The diagram below shows one possible method for determining the Young modulus of a metal in the form of a wire.Practical Apparatus Worked Example, downloadable AS & A Level Physics revision notesDescribe how you can use this apparatus to determine the Young modulus of the metal. The sections below should be helpful when writing your answers.

  • The measurements to be taken.
  • The equipment used to take the measurements.
  • How you would determine Young modulus from your measurements.

Step 1: State the necessary measurements to be taken

    • The diameter of the wire
    • The initial length of the wire
    • The extension of the wire (final length – initial length)
    • The mass of the hanging masses or the weight applied to the wire

Step 2: State and explain which equipment would be the most suitable

For measuring the diameter of the wire:

    • A micrometer screw gauge or vernier callipers
    • Micrometer would be best as this has the highest resolution when measuring small areas

For measuring the original length / extension of the wire:

    • A metre ruler or a tape measure
    • The wire has a moderate length which cannot be measured using a vernier scale

For measuring extension:

    • Travelling microscope
    • These are designed for measuring small changes in length

For measuring the mass:

    • Scales or a top-pan balance
    • A top-pan balance would be best as this has the higher resolution
    • W = mg equation can be used to calculate weight

For measuring the weight directly:

    • A newton-meter
    • This is useful if ‘known’ weights are used and to check if the quoted masses are accurate

Step 3: Explain how Young's modulus can be determined from these measurements

    • Young modulus is equal to the gradient of a stress-strain graph (in the linear region)
    • Stress is equal to:

Tensile Stress Equation
    • Strain is equal to:

Tensile Strain Equation

Where:

    • F = weight (N)
    • A = cross-sectional area of wire (m2)
    • ΔL = extension (m)
    • L = original length (m)

  • Young's modulus for this metal is then calculated using the following equation:

Young's modulus using graph, downloadable AS & A Level Physics revision notes

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Katie M

Author: Katie M

Expertise: Physics

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.