Magnetism

• • Permemnant magnet: prodcues its own magnetic field
• Bar magnets have two ends- they are called poles

  • magnetic forces are strongest at the poles
  • 2 like poles repel = force of repulsion
  • 2 unlike poles attract eachother
  • attraction n repulsion = non-contact
• Induced magnet: becomes a magnet when placed in a magnetic field 

  • Always causes a force if attraction. 
  • If you take away the permanent magnet then induced magnet loses most of all of their magnetism quickly
• • Four types of magnetic material: iron, steel (alloy of iron), cobalt, nickel: can be made into permanent of induced magnet 
• the closer the magnet the stronger the force viseversa
• magnetic field diagram?


  DRAW

  
• When current flows through conduction wire a magnetic field is produced around the wire 
• • If you change direction of the current, you change the direction of the magnetic field 
• how to increase the strength of magnetic field?

  • increase number of coils
  • a solenoid
  • iron core
  • increasing current
• shows you the direction of conventional current

  
• Electromagnetic are useful as you can change the strength of the magnetic field by changing size of the current. and turn it on n off
• what is the motor effect?

  A wire carrying a current creates a magnetic field. This can interact with another magnetic field, causing a force that pushes the wire at right angles
• how does the motor effect work

  • Magnetic field around wire interacts with magnetic field between magnets and the wire experiences a force in the upwards direction, causing the wire to move upwards (this is the motor effect)
• If the conductor is parallel to the magnetic field it will not experience a force

  
• To determine direction of the force, use Flemings left hand rule

  
• How does an electric motor work?

  • current in the left-hand side of the coil causes a downward force, and current in the right hand side of the coil causes an upward force;
  • the coil rotates anticlockwise because of the forces are in opposite directions;
  • each side of the coil is now near the opposite magnetic pole.

  
• why is the split ring commutator important?

  every half second it changes the direction of current
• electric motor

  The speed of rotation of the coil can be increased by:

  • increasing the size of the current;
  • using a stronger magnet;
  • increasing the number of turns of wire in the coil;
  • reducing friction between the coil and the axel it rotates on