# 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

• 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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