Resistance and Light Circuits

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Circuits - The Basics

Current is the rate of flow of charge around a circuit. Current will only flow through a component if there is a voltage across that component.

Voltage is the driving force that pushes the current around.

Resistance is anything in the circuit which slows the flow down.The more components to the circuit, there will overall be a higher resistance.

  • When you increase the voltage- then more current will flow.
  • If you increase the resistance- then the less current will flow.

Ammeter- Measures Current

  • Must be placed in series anywhere in the main circuit, but never in a parallel like a voltmeter.

Voltmeter- Measures Voltage

  • Must be placed in parallel around the component under test.
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Voltage-Current Graphs

  • A metal filament lamp - the temperature of it increases, the resistance increases hence the curve.
  • A diode - lets the current flow one direction 
  • A resistor can have different resistances hence they may have different slopes.


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Series and Parallel Circuits

Series Circuits

  • The different components are connected in a line.
  • You cannot control which components current flows through.
  • If you disconnect one component, the circuit is broken and they all stop.
  • The more components, the more resistance.

Parallel Circuits

  • Each component is separately connected to the supply.
  • If you disconnect or remove one of them, it will hardly affect the others.
  • You can add an another component by adding a loop.


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Charge= Current x Time

Q = I X t

Voltage= Current x Resistance

V = I x R

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