NEW GCSE - AQA - Physics GCSE - Topic 2 - Concise notes from Spec

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Electrical charge and current

·         For electrical charge to flow through a closed circuit the circuit must include a source of potential difference.

·          Electric current is a flow of electrical charge.

·         The size of the electric current is the rate of flow of electrical charge.

·         Charge flow, current and time are linked by the equation:

Charge ­ = current × time

·         Current has the same value at any point in a single closed loop

 

Current, resistance and potential difference

·         The current (I) through a component depends on both the resistance (R) of the component and the potential difference (V) across the component.

·         The greater the resistance of the component the smaller the current for a given potential difference (pd) across the component.

·         Current, potential difference or resistance can be calculated using the equation: potential difference  = current × resistance

 

Series and parallel circuits

·         There are two ways of joining electrical components: in series and in parallel.

·         Some circuits include both series and parallel parts.

·         For components connected in series:

-       There is the same current through each component

-       The total potential difference of the power supply is shared between the components

-       The total resistance of two components is the sum of the resistance of each component. Rtotal = R1 + R2

·         For components connected in parallel:

-       The potential difference across each component is the same

-       The total current through the whole circuit is the sum of the currents through the separate components •

-       The total resistance of two resistors is less than the resistance of the smallest individual resistor.

 

Direct and alternating potential difference

·         Mains electricity is an ac supply.

·         In the UK the domestic electricity supply has a frequency of 50 Hz and is about 230 V.

 

Mains electricity

·         Most electrical appliances are connected to the mains using three-core cable.

·         The insulation covering each wire is colour coded for easy identification:

-       Live wire = brown

-       Neutral wire = blue

-       Earth wire = green and yellow stripes.

·         The live wire carries the alternating potential difference from the supply. The potential difference between the live wire and earth (0 V) is about 230 V.

·         The neutral wire completes the circuit. The neutral wire is at, or close to, earth potential (0 V)

·         The earth wire is a safety wire to stop the appliance becoming live. It’s at 0 V, it only carries a current if there is a fault.

Power

Power = potential difference × current

Power = (current) ² × resistance

 

Energy transfers in everyday appliances

·         The amount of energy an appliance transfers depends on how long the appliance is switched on for and the power of the appliance.

·         Work

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