# Current electricity

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• Created by: Holly45
• Created on: 23-03-15 19:51

## Parallel circuits

• each component is separatly connected to the positive and negative of the supply
• if you disconnect one of the components it will hardly affect the others
• all the components get a full source of voltage so the voltage is the same all the way across (V1 = V2 = V3)
• the total current is equal to the total of all the currents though the separate components (A = A1 + A2 + A3)
• there are junctions where the current splits and rejoins
• the total current going into a junction has to equal the total current leaving
• ammeters are always connected in series even in a parallel circuit
• voltmeters are always connected in parallel even in series
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## Series circuits

• connect in a line between the negative and positive of the power supply
• if you remove or disconnect one component the circuit is broken
• the total P.d of the supply is shared between the various components
• the voltage around a series circuit always adds up to equal the sources voltage (V = V1 + V2 + V3)
• the same current flows through all parts of the circuit (A1 = A2)
• the total resistance is the sum of all resistances (R = R1 + R2)
• the bigger the resistance of a component then there is a bigger share of the total P.d
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## Circuit devises

• current only flows though a diode in one direction
• light emitting diodes are useful and they only have a small current
• an LDR is a resistor that is dependant on light
• the resistance of a thermistor decreases as the temperature increases
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## Resistance

• voltage and current graphs show how the current varies as you change the potential difference
• filament lamp graph shows as the temperature increases the resistance increases
• a diode only lets the current flow in one direction
• resistance increases with temperature
• P.d = current X resistance (V = I x R)
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## Circuits

• the ammeter measures the current flowing though the component and must be placed in series
• the voltmeter measures the potential difference and must be placed in parallel
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## Current and potential difference

• current is the flow of electrical charge
• it will only flow if there is a potential difference across it
• potential difference is the force that pushes the current around
• resistance is anything in the circuit which slows the flow down
• the greater the resistance, the smaller the current flows
• current = charge (divided by) time (Q = I x T)
• potential difference across an electrical component is the energy that is transferred by the electrical component per unit of charge
• P.d = work done (divided by) charge
• W = V x Q
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## Static electricity

• caused by friction
• when insulating materials are rubbed together, negatively charged electrons will be scraped off one and dumped on the other
• this leaves a positive static charge on one and a negative charge on the other
• electricity charged objects attract small objects placed near them
• both negative and positive electrostatic charges are only ever produced by the movement of electrons
• positive charges are caused by electrons moving away
• two things with opposite electrical charges are attracted to each other
• electrical charges can move easily though some metals known as conductors
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