electromag

• field

  area magnet feel force
• current in wire

  circle field around
• microphone

  1. sound wave hit diaphragm
  2. coil move in permanent field
  3. generate current
  4. frequency/ amplitude determins current
• induced

  only magnetic in field
• permanent

  made of magnetic mat, produce own field
• test for magnetism

  see if repel other magnetic mat= permanent
• detect field (compass)

  1. put near magnet on paper (mark direct point)
  2. move around field (join lines)
• compass theory

  1. if no magnet, n attract s, point in direct
  2. point to n, earth centre is magnetic, gen own field
• solenoid

  wire coil, current flow

  inside- strong/ uniform

  outside- similar to magnet
• solenoid+ iron core

  electromag
• motor effect

  1. wire- carry current
  2. cause field to interact
  3. exert force 90
• LHR

  first finger- field

  middle- current

  thumb- force
• horseshoe magnet

  1. shows direction of force
  2. rail in magnet, bar on top
  3. generate force, rolls bar
• motor

  1. force act both sides coil
  2. one act up/ down (rotate)
  3. split-ring comutator swaps +/- every 1/2 turn
  4. can be reversed by changing polarity of DC
• loudspeaker

  1. AC flows in coil= field
  2. interact with permanent field
  3. exert force
  4. coil goes back/ forth
  5. alternate field= vibrate
  6. cause pressure (sound)
• generator effect

  1. induce PD in wire relative to field
  2. magnet in coil/ wire in field, move opposite direction
  3. PD change
  4. keep changing PD= AC