Electricity

  • Created by: 03Louise
  • Created on: 24-04-18 18:23
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  • Electricity
    • Current
      • Flow of electrical charge
        • Only does so when there's a potential difference and the circuit is complete
      • Slowed down by resistance
        • ohms
      • Charge= current x time
    • Potential difference
      • Energy transferred= charge moved x potential difference
      • Voltage
      • Potential difference= current x resistance
    • Resistance
      • Increases with temperature
        • Electrons collide with ions in the lattice giving them energy causing them to vibrate/ heat up
          • Lead to it being harder for ions to get through
        • Too hot- no current
    • Circuit devices
      • Resistors
        • Current is directly proportional to p.d.
      • Filament lamp
        • Curved current/p.d. graph
      • Diode
        • No negative flow (high resistance)
      • Light Dependent Resistor (LDR)
        • Resistance is dependent on light
        • Night lights, outdoor lighting, burglar detectors
        • Hot= low resistance
      • Thermistor
        • Cold= high resistance
        • Car engine temperature detectors, electronic thermostats
    • Circuits
      • Series
        • Doesn't work if one part is removed
        • More cells= bigger supply p.d.
        • Current is the same everywhere
        • More resistors= increased resistance
      • Parallel
        • If one thing is disconnected the circuit can still work
        • How most things are connected
        • Everyday circuits contain a mix
        • All components have the same p.d
        • Current is shared between branches
        • If you add a second resistor in parallel to a series circuit overall resistance decreases to less than the smallest resistor
          • Because the current has more than one direction to go in
      • Energy
        • When there's a p.d. energy is transferred as work is done against resistance
          • Energy is supplied by the power source which is given up when going through components because of resistance
            • Large p.d.- more energy is transferred
        • E=IxVxt
        • Kettle
          • Transfer electrical energy to the thermal store
        • Fan
          • Electrical energy from the battery is transferred to the kinetic store
        • Heating
          • Temperature is too high- circuit melts
            • Fuses use this to protect circuits
          • Toasters use high resistance to heat up wires in the toaster creating infrared radiation
        • Power
          • Circuits
            • Series
              • Doesn't work if one part is removed
              • More cells= bigger supply p.d.
              • Current is the same everywhere
              • More resistors= increased resistance
            • Parallel
              • If one thing is disconnected the circuit can still work
              • How most things are connected
              • Everyday circuits contain a mix
              • All components have the same p.d
              • Current is shared between branches
              • If you add a second resistor in parallel to a series circuit overall resistance decreases to less than the smallest resistor
                • Because the current has more than one direction to go in
            • Energy
              • When there's a p.d. energy is transferred as work is done against resistance
                • Energy is supplied by the power source which is given up when going through components because of resistance
                  • Large p.d.- more energy is transferred
              • E=IxVxt
              • Kettle
                • Transfer electrical energy to the thermal store
              • Fan
                • Electrical energy from the battery is transferred to the kinetic store
              • Heating
                • Temperature is too high- circuit melts
                  • Fuses use this to protect circuits
                • Toasters use high resistance to heat up wires in the toaster creating infrared radiation
              • Power
                • Power(w)= Energy transferred(J) /Time(s)
                • Energy transferred a second
                • Power ratings
                  • Energy transferred a second
                  • Higher=more energy transferred a second/ uses more energy
                • Power(w)= Current(A) x p.d(V)
                  • P=IV or P=I^2V
                  • Use to work out the fuse needed-just a little higher
          • Power(w)= Energy transferred(J) /Time(s)
          • Power ratings
            • Higher=more energy transferred a second/ uses more energy
          • Power(w)= Current(A) x p.d(V)
            • P=IV or P=I^2V
            • Use to work out the fuse needed-just a little higher
    • Home
      • Mains=a.c. (alternating current)
        • Constantly changes direction
        • 230V, 50Hz
      • Cables
        • Neutral
          • Blue
          • 0 V
          • Completes the circuit, flows out
        • Live
          • Brown
          • +/- 230 V
          • Causes electrical shocks
            • Body provides a path of low resistance to the earth- large p.d.
            • Can cause fire
        • Earth
          • Green/yellow
          • 0 V
          • Carries away current if something goes wrong
            • Appliance becomes live- prevents electrocution
          • Untitled
          • Only in appliances with metal casing
      • Fuses
        • Prevent surges which can cause melting, fire and electric shocks
        • Live wire touches case
          • Current flows through earth wire
            • Creates a surge causing the fuse to melt breaking the circuit
              • Prevents fires and electric shocks
        • Household fuses
          • Protect wiring in the house
        • Circuit  breakers
          • Work in the same way
            • Large currents "trip" the fuse
            • Can be reset, quicker but more expensive
      • Large current =larger cable needed

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