Section 2- Electricity

Static Electricity
1. Conductors= materials which allow the flow of electric charge (metals)
  1. Insulators= materials which do not allow the flow of electric charge (plastic)
2. Static electricity is the build up of electric charge through friction. It is 'static' because the charge is unable to move
3. The Atom:
4. ELECTRONS MOVE, PROTONS DON'T MOVE!
5. When two INSULATING materials are rubbed together, electrons will be taken off one and MOVE to the other
  1. This will leave a POSITIVE electrostatic charge on one and a NEGATIVE electrostatic charge on the other
    1. With the POLYTHENE ROD electrons move from the duster to the rod, therfore the ROD becomes NEGATIVELY CHARGED and the DUSTER is left POSITIVELY CHARGED.
    2. With the ACETATE ROD electrons move from the rod to the duster, therfore the DUSTER becomes NEGATIVELY CHARGED and the ROD becomes POSITIVELY CHARGED
6. Experiments
  1. Gold-Leaf Electroscope
  2. Suspending a charged rod
  3. Van de Graaff Generator
Charge, voltage and energy change
1. Charge through a circuit depends on CURRENT and TIME
  1. Charge = Current x Time
  2. Charge= Coulombs (C)
2. VOLTAGE is the ENERGY TRANSFERRED per UNIT OF CHARGE PASSED
  1. ONE VOLT is ONE JOULE per COULOMB
3. Batteries provide energy but also push the charge around a circuit. The charge carries the energy. Thgis is represented by the pizza model.
  1. Pizzeria= Battery Party= Lamp Pizza= Energy Delivery Man= Charge
Series and Parallel Circuits
1. Series Circuit
  1. All components connected in one loop, if one component in removed the circuit breaks and stops working
  2. Christmas tree lights are often only series circuits
2. Parallel Circuit
  1. Our houses are often wired up with parallel circuits
  2. Each component is separately connected to the energy supply. If one component is disconnected it shouldn't disrupt the rest of the circuit.
Circuit Symbols
Resistance
1. Thermistors
  1. Temperature-dependent resistor
  2. In hot conditions the resistance decreases
  3. In cool conditions the resistance increases
2. LDR's
  1. Light-dependent resistor
  2. In bright light the resistance decreases
  3. In darkness the resistance increases
3. Resistance changes depending on the voltage and current
  1. Voltage = Current x Resistance
Basic Circuits
1. Current= the flow of charge round the circuit. Current will only flow through a componant if there is a voltage across it. (A)
2. Voltage= the driving force that pushes the current round. (V)
3. Resistance= anything in the circuit which slows the flow down. More componants= more resistance. (Ohms)
4. If you increase the voltage, more current will flow. If you increase the resistance, less current will flow.
5. Ammeter= measures current (A) flowing through a componant. It must be placed in series in the circuit
6. Voltmeter= measures the voltage (V) across a componant. It must be placed in parallel around the componant, not around the variable resistor or battery though!
Energy and power in circuits
1. Electrical power is the rate at which an appliance transfers energy
  1. High power rating=high energy transfer in short time
    1. Large current
  2. Electrical Power = Current x Voltage
  3. Appliances show their power and voltage ratings, so do fuses
2. Electrical appliances transfer electrical energy
  1. When current flows through a componant, energy is transferred
  2. Energy Transferred= Current x Voltage x Time
Fuses and Circuit breakers
1. Earth Wires
  1. If a fault develops in the circuit and the appliance has metal casing (e.g. toaster) then the electrons may want to jump onto the metal and up your arm giving you a shock. However the earth wire stops this happening because the electrons go down that as it is a more direct route in their circuit.
  2. Usually has no current, purely for safety uses
2. Fuses
  1. When a fault occurs and the earth wire comes into use, there will be a large surge of current run through the fuse which will melt at a certain point and so cut off the appliance from the live wires making it safer
3. Circuit Breakers
  1. Electrical safety device used in some circuits, like a fuse they protect the circuit from damage if too much current flows through it.
  2. They do not melt like fuses, they break the circuit by opening a switch when a current surge is detected
Journey of Electricity + Safe Plugs
1. Wires in the UK
  1. Live Wire= Electrical current flows down this
  2. Neutral Wire= Completes the circuit
  3. Earth Wire= Usually no current, for safety purposes
2. 1. Elecricity for your home comes from the MAINS SUPPLY
  1. 2. Electricity enters your home via an UNDERGROUND CABLE
    1. 3. Electricity flows through the ELECTRICITY METER
      1. 4. Electricity flows through a CONSUMER UNIT or FUSE BOX
        5. Electricity flows into the RING MAIN CIRCUIT
3. Direct Current (batteries)
4. Alternating Current (Mains supply) 230V 50Hz- changes direction 50 times a second

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Section 2- Electricity

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