NEW GCSE - AQA - Physics GCSE - Topic 2 - Concise notes from Spec
- Created by: IdreesAhmed1309
- Created on: 16-12-17 20:27
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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