Transformers and power

Transformers and power

1. if 100 % efficient

   • an alternating current is supplied to the primary coil
     • which produces an alternating magnetic field
       • in the iron core
         • this magnetic field links with the secondary coil
           • which induces an alternating voltage / p.d across the secondary coil

2. switch mode transformers

   • work at higher frequencies ( 50 - 2000 khz_ - much lighter and smaller than transformers working from the mains.....useful for devices like mobile phone charges...... use very little power when they are on but nothing connceted ( no load appliance)

3. motor effect

   • Electromagnets
     • when current flowing through a wire a magnetic field is produces around the wire
     • 1) switch on curcuit 1
       • the electromagnet carries a current
         • magnet gets swtiched on
           • armature made of iron get attracted
             • second circuit gets switched on
               • a low current curcuit switches on a high current circuit
     • to make electromagnet stronger
       • add iron core
       • more current
       • more coils
     • current flows through coil/electromagnet
       • magnetic field produced
         • short side of iron bar attracted to electromagnet
           • contacts pushed together by iron bar
             • starter motor curcuit completed
               • current flows through starter motor OR p.d. acroos starter motor
   • flemings left hand rule
     • thumb- movement
     • first finger - field
     • second finger - curremt
   • force can be increased by increasing current and magnetic field
   • force can be reversed by reversing the current and magnetic field