Electricity s2

• Main electricity


  Electricity generated by power stations and transported around the country through the National Grid
• Main electricity


  • Alternating current supply
  • Frequency of 50 Hz
  • Voltage of about 230 volts
• Main circuit wires


  • Live Wire
  • Neutral wire
  • Earth wire
• Live Wire


  Provides the path along which the electrical energy from the Power Station travels, carries the alternating voltage
• Neutral wire


  Completes the circuit and is kept at 0 volt
• Earth wire


  Provides a path for current to escape without passing through the user, protects against faults
• Ring main circuit


  • Allows several appliances in different parts of the same room to be connected to the mains using the minimum amount of wiring
• Plug and sockets


  Three pins for the Live Wire, neutral wire and Earth wire
• Wiring a plug


  1. Connecting wires to the correct terminals

  2. Ensuring cable is held firmly

  3. Fitting the correct fuse

  4. Connecting the three-pin plug to the appliance and then plugging into the socket
• Electrical energy comes from a generator in a power station


  Travels to the kettle
• Earth wire


  Connects the metal body of an appliance to Earth, prevents the appliance from becoming live if the live wire comes loose
• Double insulated appliances


  • Outer case is made of plastic rather than metal, providing an extra layer of insulation
• Heating effect of current

  Caused by the resistance and current passing through wires or appliances
• Wiring in a house is designed to let current pass through it easily, so the wires do not become warm when appliances are being used</b>
• Heating elements


  Wires designed to have a high resistance so that as the current passes through them, energy is transferred and the element heats up
• Electrical power


  The transferred energy per unit time, can be calculated as P = E/T
• Power of an appliance

  Related to the voltage across it and the current flowing through it, can be calculated as P = VI
• Electrical energy


  Can be calculated as E = VIt
• Fuse values


  Plugs are usually fitted with 3A, 5A or 13A fuses, the value tells you the current needed to blow the fuse
• Calculating the correct fuse for an appliance

  Use the equation P = VI to determine the current, then select the closest fuse size
• Alternating current (AC)


  Current that flows back and forth, the value increases and decreases in opposite directions
• Direct current (DC)


  Current that flows in one direction, with the same value
• Electrical hazards from mains electricity

  • Damaged insulation
  • Overheating of cables
  • Damp conditions
  • Excess current from overloading
• Electric current


  The amount of charge passing a point per second, measured in amperes
• Conductors


  Materials that allow charge to flow through them easily, usually metals
• Insulators


  Materials that do not allow the flow of charge through them easily, such as plastics, rubbers, glasses or woods
• Voltage


  The transfer of energy per unit charge, measured in volts
• Voltmeter


  • Measures the voltage across a component or circuit, connected in parallel
• Series circuit


  • A simple loop circuit with no branches or junctions, current is the same in all parts
• Parallel circuit


  • A circuit with branches or junctions, providing more than one path for the current to follow
• Resistance


  Measured by comparing the size of the current and the voltage applied across a component
• The currents entering a junction must always be equal to those that leave at the junction
• The current that enters a junction is 0.6 amp and the current that leaves is 0.4 amp + 0.2 amp = 0.6 amp
• Each branch of the circuit receives the same voltage, so if more bulbs are added to a circuit in parallel they all keep the same brightness
• The voltage remains the same across each branch and is equal to the voltage across the cell or battery
• The lights in your home are wired in parallel, this is why you can switch lights on and off separately and the brightness remains unaffected when other lights are turned on or off
• If a bulb breaks or is removed you can still use the other lights
• Resistance


  We measure the resistance R of a component by comparing the size of the current I in that component and the voltage V applied across its ends
• Voltage, current and resistance


  Voltage V in volts equals resistance R in ohms times current I in ampere
• Ohm


  1 ohm is 1 volt per ampere