Testing Series & Parallel Circuits (OCR Gateway GCSE Physics: Combined Science)

Revision Note

Test yourself
Ashika

Author

Ashika

Last updated

Testing Series & Parallel Circuits

  • The GCSE examination will require an understanding of the variation of resistance in the following devices:
    • Filament lamps
    • Diodes
    • Thermistors
    • LDRs

  • Luckily, the design and use of the circuits to investigate how resistance varies is broadly similar for each component

  • It is important to recognise that:
    • Voltmeters are always connected in parallel with the component they are measuring the potential difference of
    • Ammeters are always connect in series with the rest of the components in the circuit

Resistance in Filament Lamps & Diodes

  • In order to investigate the variation of resistance in a filament lamp or diode, the following circuits should be set up:
  • The current is the independent variable
    • The variable resistor is used to change the current flowing through the filament lamp / diode

  • The voltage is the dependent variable
    • The voltmeter is used to measure the voltage across the filament lamp / diode

  • Calculate the resistance of the filament lamp / diode for each chosen value of current and measured value of voltage using the equation:

Investigation of Current and Voltage, downloadable IGCSE & GCSE Physics revision notes

These circuits enable the variation of resistance in a filament lamp or a diode to be investigated

Resistance in LDRs & Thermistors

  • In order to investigate the variation of resistance in a LDR or a thermistor, the following circuits should be set up:

LDR & Thermistor Circuits, downloadable IGCSE & GCSE Physics revision notes

These circuits enable the variation of resistance in a LDR or a thermistor to be investigated

  • For the LDR circuit:
    • Begin with the lamp turned off in a dark room
    • Record the reading on the voltmeter and ammeter
    • Slowly increase the light intensity of the lamp using the dimmer switch
    • Record the reading on the voltmeter and ammeter for each increase in light intensity

  • For the thermistor circuit:
    • Begin with the heater turned off
    • Record the reading on the voltmeter and ammeter
    • Slowly increase the temperature of the heater using the dimmer switch
    • Record the reading on the voltmeter and ammeter for each increase in temperature of the heater

  • In both situations, make sure the lamp and heater are close, but not touching, the LDR and thermistor respectively
  • Wait a few seconds before taking the voltmeter and ammeter readings to allow the LDR and thermistor to react to the change in the environment
  • Calculate the resistance of the LDR or thermistor for each change in light intensity or temperature using the equation:

Examiner Tip

It's really common for examiners to test your understanding of setting up and using a circuit to measure current, voltage and resistance of a component. Generally, make sure the following are included in your circuit diagrams:

  • The ammeter is connected in series to the component
  • The voltmeter is connected in parallel to the component
  • The component with the appropriate circuit symbol
  • If you need to vary the current, include a variable resistor
  • The component is connected to a power supply with a low voltage (below 15 V) otherwise too high a current in the circuit will start to affect the resistance of the component

IV-circuit, IGCSE & GCSE Physics revision notes

Circuit diagram for measuring the variation of resistance of a component, using current and voltage

You've read 0 of your 5 free revision notes this week

Sign up now. It’s free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Ashika

Author: Ashika

Expertise: Physics Project Lead

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.