Electricity 2

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  • Created by: Ebod
  • Created on: 28-07-21 22:09
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  • Electricity 2
    • Household Electricity / Mains
      • three-core cables
        • copper core, insulating plastic coating
        • Live Wire
          • 230 V from mains supply
          • can be fatal if touched due to p.d
          • connected to fuse
          • brown
          • humans = 0 V, so p.d of 230 V, current would run through us
            • electric shock/ electrocution
        • Earth Wire
          • 0 V
          • Prevents appliance from becoming live
          • green and yellow
        • Neutral Wire
          • blue
          • around earth potential (0 V)
          • completes the circuit by carrying away charge
      • oscilloscope
        • frequency = number of cycles (from peak to peak) / how long it took
      • UK mains supply
        • 50 Hz, 230 V
        • AC supply (alternating current)
          • current switches direction
      • DC (direct current)
        • current always flows same direction
        • batteries and cells
      • power
        • work is done electrically when current flows in a circuit
          • this electrical energy can be transferred into other energy stores
            • mostly dissipated as thermal
            • e.g thermal for a kettle or kinetic for a fan
        • P = E / t
        • E = QV
        • P = VI
        • P = I^2 R
        • Watt = Joule / second
      • National Grid
        • power station
          • step-up transformer
            • p.d. increased to increase power
              • upto 400,000 V
                • P = VI
                  • more voltage = less current
            • powerline
              • step-down transformer
                • consumer
                • p.d decreased to 230 V, safer for home use
                  • high p.d blows appliances
              • Transports current at very high voltages
                • pylons; thick insulating wires
                  • P = I^2 R
                    • low R + low I = less P Lost
        • run well below maximum power output
          • spare capacity if there's high demand
        • system of cables and transformers, transferring electrical power
          • power stations (supply) to consumers (demand)
        • high voltage, low current
          • high current causes energy dissipation (heat)
            • Untitled
    • Electrical Safety
      • earthing
        • provides alternative pathway for current if there's a fault
        • if casing becomes live, current will flow through casing down earth wire,
          • causing a lot of current, fuse will melt in live wire, cutting off electricity to appliance
      • fuse
        • thin piece of wire
        • melts from surges or when current gets to high
          • breaks circuit when melted, no current can flow
        • e.g appliance that usually has 3A current may have 5A fuse
        • simple
        • permanently broken after single surge
        • cheap
        • must be replaced after surge
      • circuit breaker
        • gets tripped from surges or when current gets to high
          • turns off circuit, no current can flow
        • can be reset; multiple uses
        • more expensive than fuses
      • surge
        • sudden increase in current
        • due to change in circuit
          • e.g turning on or off an appliance / component
        • due to a fault in the circuit
        • due to unexpected interruption to current / voltage
          • e.g lightening
        • can cause fires, electric shocks or casing to become live
      • double insulation
        • covered in plastic casing
          • no exposed metal parts
        • only live and neutral wire
        • plastic doesn't conduct electricity
          • no electric shock

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