OCR AS Physics

Revision Notes

1.3.6 Circuits

Constructing Circuits

  • Constructing, designing and checking circuits are an essential practical skill in physics
  • There are some important points to consider with all circuits:
    • If the current is to be measured, an ammeter must be connected in series
    • If the potential difference is to be measured, a voltmeter must be connected in parallel to the required component
    • If the current is to change between two paths (eg. charging and discharging a capacitor) a switch must be present
    • A diode must always be facing the direction of the current flow
    • Make sure each component is able to handle the amount of current in the circuit. Otherwise, they could fuse, be damaged, or spark

Circuit Construction, downloadable AS & A Level Physics revision notes

Circut with corresponding circuit diagram


  • The polarity of an electrical component means that it will function differently depending on the direction in which it is connected
    • In other words, a non-polarised components, such as a lamp can be connected in any direction it will still light up
  • A polarised component can only be connected in a circuit in one direction
    • If not, it will either not work, work incorrectly or break
  • Common polarised electrical components include:
    • Cell / batteries / any power supply
    • Diodes
    • LEDs (light-emitting diodes)
    • Electrolytic capacitors
  • The positive and negative terminal on a battery is normally clearly marked
    • If not, the negative side has a larger metal area
  • LEDs, and diodes consist of two pins or ‘legs’
    • The longer leg is the positive (anode) pin
    • The shorter leg is the negative (cathode) pin
  • The polarity can sometimes be checked by multimeters and leads connected to the appropriate pins

LED polarity, downloadable AS & A Level Physics revision notes

Polarity of an LED is shown by the longer or shorter pin

Exam Tip

Remember to always keep the number of wires, leads and crocodile clips to a minimum. Otherwise it can become confusing as to which component is connected to which in a practical experiment

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Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.

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