A LevelPhysicsOCRRevision Notes1. Development of Practical Skills in Physics1.1 Experimental Design1.1.2 Control Variables

Control Variables (OCR A Level Physics)

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Identifying Control Variables

Types of Variables

  • In an experiment, a variable is any factor that could change or be changed
  • There are different types of variables within an experiment
    • The independent variable: the only variable that should be changed throughout an experiment
    • The controlled variables: any other variables that may affect the results of the experiment that need to be controlled or monitored
    • The dependent variable: the variable that is measured to determine the outcome of an experiment (the results)

  • It is essential that any variable that may affect the outcome of an experiment is controlled in order for the results to be valid
  • Preliminary research and preliminary studies can be used to identify variables within an experiment and to determine ways of controlling these variables effectively
  • The science surrounding the issue / problem being investigated is likely to contain information about different factors or variables that may exist

Identifying Control Variables: An Example - Science Surrounding Ideal Gases

  • There are several experiments that can be carried out to investigate the properties of ideal gases
  • Factors that can be changed include:
    • Temperature
    • Pressure
    • Volume
    • Number of moles of gas

  • The key point with ideal gas experiments is to ensure that only one of these variables is changed during a particular experiment
    • This is known as the independent variable

  • All other variables must be controlled (they must stay the same)
    • These are known as the control variables

  • When investigating Charles’ law:
    • The temperature is varied (independent variable)
    • The volume is measured (dependent variable)
    • The pressure and number of moles must be kept the same (control variables)

  • When investigating Boyle’s law
    • The pressure is varied (independent variable)
    • The volume is measured (dependent variable)
    • The temperature and number of moles must be kept the same (control variables)

  • If these control variables are not kept constant, they could affect the results of the experiment
    • This would make the results unreliable

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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.