Reducing Errors (Edexcel International A Level Physics)

Revision Note

Katie M


Katie M



Reducing Errors

  • Reducing errors in an experiment is vital for obtaining more accurate results
  • Even if the experimental result is close to the true value, there are always potential limitations of experimental methods such as the presence of random errors
  • Random errors cannot be completely removed but their effect can be reduced by taking as many repeats as possible and using the average of the repeats
  • There are always opportunities to identify limitations of the procedure, some common examples include:
    • Parallax error when reading scales
    • Not using a fiducial marker (eg. when measuring the time period of a pendulum using a stopwatch)
    • Not repeating measurements to reduce random errors
    • Not checking for zero errors to reduce systematic errors
    • The equipment not working properly or not checking beforehand with small tests
    • Equipment with poor precision and resolution (eg. using a ruler over a micrometer)
    • Difficult to control variables (eg. the temperature of the classroom)
    • Unwanted heating effects eg. in circuits

  • Parallax error is minimised by reading the value on a scale only when the line of sight is perpendicular to the scale readings (i.e.. at eye level)
  • Examples of where parallax error is common are:
    • Determining the volume of liquid
    • Making sure two objects are aligned
    • Reading the temperature from a thermometer
  • If it makes it easier, use a marker to help where possible

Parallax Error

Reading the value of the needle head-on (left image) looks different to reading it from the right (right image). This is parallax error 

  • A fiducial marker is a useful tool to act as a clear reference point, such as when measuring the time period of a pendulum using a stopwatch
  • This improves the accuracy of a measurement of periodic time by:
    • Making timings by sighting the pendulum as it passes the fiducial marker
    • Sighting the pendulum as it passes the fiducial marker at its highest speed. The pendulum swings fastest at its lowest point and slowest at the top of each swing

Fiducial marker, downloadable AS & A Level Physics revision notes

A fiducial marker is used to mark the centre of the oscillation of the pendulum

  • Zero errors must be checked for in both digital and analogue instruments
    • E.g., If there is no current through the circuit, an ammeter must read 0 A
  • The common way to reduce unwanted heating effects in circuits is to turn off the power supply in between readings
    • As the temperature of a component increases, so does its resistance (e.g., in wires). This will affect the experiment and produce an error in your final result

Worked example

A student wants to determine the radius of a wire for an experiment to calculate its Young Modulus. They measure the radius using a ruler from one part of the wire.

Discuss ways in which the student can reduce the error in this reading.

1. Comment on the instrument used

    • Since the radius of a wire is on the order of < 1 mm, and has a circular cross section, a micrometer screw gauge should have been used instead

2. Comment on the method

    • The student did not take any repeat readings
      • They should take between 3-5 repeat readings for each value of the radius from the micrometer

3. Suggest improvements to the method

    • The experiment assumes the wire is uniform the whole way through (i.e. has the same radius)
    • This can be checked by measuring the radius at different points on the wire 

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Katie M

Author: Katie M

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.

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