Magnetism

• Magnets should be drawn like this:

  • From South to North
  • In through the SOUTH Pole, out through the NORTH Pole

  A) Out

  B) In

  
• The denser the Magnetic Field Lines in a magnet are, (the closer they are) the stronger the Magnetic Field will be in that area
• • A compass lines up with the field lines of any magnetic field its put in
  • The red side of a compass will always point towards the South Pole

  
• Two magnets of the same pole will repel against each other as the interaction of the field lines clash against each other

  
• Examples of Magnetic MATERIALS (objects influenced and can become magnets themselves) ---- [NICS!]

  • Nickel
  • Iron
  • Cobalt
  • Steel (alloy)
• Permanent Magnets are magnets which produce their own magnetic field all the time
• Induced/Temporary Magnets are materials which only have a magnetic field temporarily

  -

  When a material is placed within the magnetic field of a Magnet, the material is induced, and develops its own North and South poles. The material has been Induced.
• [Magnetically Soft Materials] Materials which LOSE their Induced Magnetism QUICKLY, like Iron or Nickel
• [Magnetically Hard Materials] Materials that KEEP their Induced Magnetism PERMANENTLY, like Steel
• SOLENOID:

  • The Magnetic Field within a solenoid is strong and uniform
  • It is only magnetic for as long as you keep the current flowing through the wire

  
• How to INCREASE an Electromagnet's STRENGTH:

  1. Increase the current [c] that flows through the solenoid
  2. Increase the number of turns [t] in a coil, keeping the same length
  3. Decrease the length [L], keeping the same number of turns
  4. Add an Iron Core. It is a soft magnetic material, so it will become an induced magnet, increasing the Electromagnet's strength
• [The MOTOR Effect]

  • A current carrying wire will produce its own magnetic field.
  • If we placed the wire in between the north and south poles of a magnet (which have their own magnetic field) then the two magnetic fields will interact.
  • This interaction results in a force exerted on the wire, which may push it out of the field

  -

  To experience the full force, the wire has to be at a 90 Degree Angle to the magnetic Field of the poles

  
• [1] ELECTRIC MOTORS:

  Because the Left side of the coil experiences an UPwards force, and the Right side experiences a DOWNwards force, the coil will rotate in a clockwise direction

  
• [2] ELECTRIC MOTORS:

  • Once the coil flips by 180 Degrees, the Current is then shown to flow in the opposite direction, so the Forces acting on each side will also flip in opposite directions
  • The coil will now start to turn in an anticlockwise direction, right back to where it started
  • If we kept it like this, the coil would just keep flipping back and forth, because the forces keep swapping around

  It would never fully turn 360 Degrees!!

  
• [3] ELECTRIC MOTORS:

  To stop the coil from flipping back and forth, we need to change the direction of the current every half turn

  So, we'll use a Split Ring Commutator, which swaps the positive and negative connections every half turn, (changing the direction of the current too)

  So the forces acting on the coil will ALWAYS rotate the coil in the same direction

  
• How a Split Ring Commutator works:

  • The split-ring commutator swaps the Positive and Negative terminals every half turn
  • Therefore, the direction of the current flowing through the coil reverses every half turn
  • This means that the forces acting on the coil will always be acting in the same direction

  This causes the coil to rotate continuously in one direction

  
• The Generator Effect (Electromagnetic Induction):

  As we move the wire through the Magnetic Field, we will INDUCE a Potential Difference in the Wire

  BUT:

  • When it STOPS moving, the Potential Difference DISAPPEARS, because there is no change in the Magnetic Field
  • The direction of the Potential Difference SWAPS everytime we CHANGE DIRECTION (push it up and down)

  
• The Generator Effect (Electromagnetic Induction):

  If we completed the wire to make it a Coil, the induced Potential Difference would generate a CURRENT.

  • This is because the Electrons would be able to flow around the circuit
  • (The Current still CHANGES DIRECTION as it moves up and down)

  
• How to change the SIZE of the Induced Potential Difference: (Generator Effect)

  • Change the STRENGTH of the Magnetic Field
  • Move the Wire or Magnets more QUICKLY
  • Shape the Wire into a Coil with MORE TURNS

  A) Strength

  B) Magnetic

  C) More Quickly

  D) Change

  E) Coil

  F) Turns

  
• [Electromagnetism] (Earlier on in CGP)

  • A Current-Carrying Wire Creates a Magnetic Field

  The LARGER the electric current, the STRONGER the Magnetic Field

  --> Use the RIGHT HAND RULE to find the direction of the Magnetic Field using the direction of the Current

  A) Concentric

  B) Magnetic

  C) Bar Magnet

  D) Current

  
• [The MOTOR Effect] A Current-Carrying Wire will experience a FORCE, when its placed INBETWEEN a Magnetic Field