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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Electricity

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