Physics module 2- Electricity

Physics module 2- Electricity

1. The Dynamo effect

   • Electromagnetic Induction
     • the creation of a voltage (and maybe current) in a wire which is experiencing
       • a CHANGE in magnetic field
         • using EM induction to transform kinetic energy into electrical energy is called the dynamo effect
           • two different situations where you get EM induction
             • An electrical conductor
               • moves through a magnetic field
               • a coil of wire is often used
             • The magnetic field
               • through an electrical conductor changes
                 • gets bigger or smaller or reverses
             • if the direction of movement is reversed then the voltage/current will be reversed too
               • to get a bigger voltage and current you can increase
                 • strength of magnet
                   • number of turns on the coil
                     • the speed of movement
           • in a power station-KE provided by turbine

2. Generators

   • Generators move a coil in a magnetic field
     • every half a turn the current in the coil swaps direction
       • therefore produces an alternating current
         • turning the coil produces not only more peaks
           • but a higher voltage and current too
             • frequency is measured in hertz
               • UK supplies electricity at 50Hz- rotating 50 times a second
                 • dynamos on bikes work slightly differently
                   • usually rotate the magnet near the coil
                     • but still use EM induction
               • number of cycles per second

3. supplying electricity efficiently

   • electricity is transformed to a high voltage before distribution
     • to transmit a lot of electrical power need a high voltage or current
       • however this means the cables get hot-inefficient-waste energy
         • before distributed the voltage is transformed to 400 000 v -low and less energy wasted
           • step up transformer-increases voltage-cheapest way
             • pylons with huge insulators as well
               • step down transformers then bring voltage down to safe levels before being distrbuted
                 • low voltage high resistance
                 • mains electricity is AC
                   • so transformers work
                     • transformers only work on AC
             • high voltage low resistance
   • power stations aren't very efficient
     • produce a lot of waste energy
       • heat loss to the environment
         • Total energy input= useful energy output+waste energy ouput
           • Efficiency= useful energy output/total energy input x 100

4. electrical power

   • running costs depend on appliances power rating
     • measure in watts or Kilo watts
       • 1 watt means 1 joule per second
         • two appliances could be running at the same time but one could be more expensive
           • this is because it consumes more energy and its energy you pay for
             • power W= voltage V x Current A
               • electricity meter records energy use in kWh
                 • this is the amount of electrical energy converted by a 1kw appliance left on for 1 hour
                   • the higher the power rating of an appliance and the longer you leave it on-more energy it consumes-more it costs
                     • energy supplied kWh= power kWh x time hours
                       • cost=number of units x price per unit
           • off peak electricity is cheaper
             • during the night is sometimes cheaper
               • storage heaters take advantage of this
                 • heat up at night and release energy slowly throughout the day
             • advantages of off-peak electricity
               • cost effective for the electricity company- power stations cant turn off-good for demand at night
                 • cheaper for consumers if they buy electricity-off peak
             • disadvantages of using off-peak
               • slightly increased risk of fire-more appliances at night
                 • start fitting your routing around cheap rate hours
                   • therefore stop enjoying the use of electricity during the day

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