transformers

• A transformer is an electrical device that can be used to increase or decrease the potential difference of an alternating current

  • This is achieved using the generator effect
• A basic transformer consists of: A primary coil, A secondary coil, An iron core (easily magnetised)

  A) iron

  B) primary

  C) magnetic field

  D) secondary

  
• • In electromagnetic induction, the coil doesn't necessarily have to physically move to cut thru magnetic field lines.
  • Instead, a changing magnetic field, eg produced by ac flowing thru a nearby coil, can induce an emf in it
  • The changing field induces a corresponding changing field in secondary coil, even if coil itself is stationary
  • so emf is induced in secondary -> generation of an ac
  • So, it's the change in the magnetic field that matters for electromagnetic induction, not necessarily the physical movement of the coil.
• • ac is supplied to the primary coil (continually changing direction -> changing magnetic field around primary coil)
  • iron core easily magnetised, so changing magnetic field passes thru it
  • so theres now a changing magnetic field inside secondary coil
  • This changing field cuts thru secondary coil and induces a pd
  • As the field is continually changing the pd induced will be alternating
  • The alternating pd will have same frequency as ac supplied to primary coil
  • If the secondary coil is part of a complete circuit it will cause an alternating current to flow
• STEP UP & STEP DOWN

  • A transformer can change size of an alternating voltage
  • They also have a other roles:

  1. increase the pd of electricity before it is transmitted across the national grid
  2. lower the high voltage electricity used in power lines to the lower voltages used in houses (safe)
  3. Used in adapters to lower mains voltage to the lower voltages used by many electronic devices

  • step up: increases pd of a power source (more turns on the secondary coil than on the primary coil)
  • step down: decreases pd of a power source (fewer turns on the secondary coil than on the primary coil)
• ELECTRICITY TRANSMISSION

  • When electricity transmitted over large distances, current in the wires heats them -> energy loss
  • electrical energy transferred @ high voltages frm power stations
  • then transferred @ lower voltages in each locality for domestic uses
  • voltage must be stepped up by a step-up transformer (after power station)
  • domestic use of electricity, lower voltage: step-down transformer (before buildings)
  • Electricity is transmitted at high voltage, reducing the current and hence power loss in the cables using transformer
• label

  A) power station

  B) up

  C) increases

  D) voltage

  E) low

  F) power loss

  G) transmision

  H) down

  I) decreases

  
• label

  A) potential difference

  B) primary

  C) secondary

  D) turns

  E) primary

  F) secondary

  G) Vp

  H) s

  I) np

  J) s

  K) ratio

  L) potential differences

  M) equal

  N) turns

  
• .There will be less rearranging to do in a calculation ifthe variable which you are trying to find is on the numerator (top line) ofthe fraction.The individual loops of wire going around each side ofthe transformer should be referred to as turns and not coils.
• label

  A) 100

  B) conservation

  C) power

  D) =

  E) p=iv

  F) ip x vp = is x vs

  G) ps = ip x vp