Circuits

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  • Created by: Katy **
  • Created on: 03-01-14 12:36

Current

  • The effect.
  • The flow of electrons around a circuit.
  • Measured in Amperes (amps) - A.
  • To meaure the ammeter is is series with the component (wire / bulb).
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Voltage

  • The drive.
  • The push given to electrons.
  • Measured in Volts - V
  • To measure have the voltmeter in parallel with component.
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Resistance

  • Opposes the current.
  • Measured in ohmns.
  • Resistance = voltage/current

Resistance of a wire:

  • metal ions arranged in a lattice
  • electrons pass through the metalbump into positive ions
  • no. of collisions = resistance of wire
  • more collisions = higher resistance
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Resistance & Current

  • A bigger resistance = electrons find it harder to pass through the metal.
  • This means there is less electrons flowing in the current.
  • increase resistance = decrease current
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Effecting Resistance

Temperature:

  • increase temperature = increase resistance
  • paricle vibrate making it harder for electrons to pass through = more collisions

Length:

  • longer = increase resistance
  • more ions = more collisions

Thickness:

  • thicker = decrease resistance
  • more electrons = less collisions

Material:

  • depends on the number of free electrons
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Current & Voltage

  • Current & voltage can be proportional
  • no gradient change = no resistance change

Same increase in voltage:

  • -smaller increase in current
  • -increase resistance

Wire at constant temperature:

  • -resistance constant
  • -increase voltage = increase current

Lamp / heater (increase temperature):

  • -increase voltage = increase current
  • increase resistance
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Variable resistor

  • Used to vary the current passing through the resistor.
  • Act as a voltage divider.

Increase resistance of varible resistor:

-increase total resitancereduces current

-increase resistors share of voltagereduces voltage across

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Electrical circuits at home

  • conected in parallel


Advantages:

  • one stops working - others will carry on
  • voltage is same for all components
  • easier to connect up circuits & to add
  • easy to work out total current drawn by parts of circiut
  • safer - each part is protected by fuse / circiut breaker / switch
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Series

  • current is the same at any point in the circuit
  • all components have the same current flowing through them
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Parallel

  • current splits when it gets to a junction in the circiut
  • no current is lost at the juction
  • total current in to the junction = total current out of the junction
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