Magnetism

• Magnets

  What is a magnet

  Magnetic materials (4)

  How to induce magnetic materials

  Hard and soft magnets

  Magnets repel and attract other magnets and attract other magnetic materials

  Iron steel cobalt nickel

  By placing them in a magnetic field

  Hard magnets - permanently magnetised

  Soft magnets - temporarily magnetised
• Magnetic field lines

  Direction

  Space Between lines

  Uniform magnetic field

  Represent the magnetic force on a north pole at a given point

  Direction shows the direction of force

  Space between the field lines show the magnitude are never touching

  Uniform magnetic field - Parallel field lines that are evenly spaces
• Electromagnetism

  Caused by

  What does an electromagnet consist off

  When an electrical current passes through a conductor it causes an electrical current

  A coil of a wire wrapped around a magnetically soft core ( can be on and off)
• Right hand grip rule

  Solenoid

  Left hand rule

  How do they affect each other?

  Determines the direction of a magnetic field produced by a current carrying wire (current is thumb )

  A wire coiled up into a spiral shape

  Left hand rule - Relative directions of force field and current

  • If current is reversed so is the field and force
  • If magnetic field or magnitude of the current is increased so will the force
• DC motors

  what is it?

  how does it work?

  Split ring commutator

  It is a coil of wire between two permanent magnets

  1. Direct current flows through the wire and it experiences a turning effect due to the forces exerted on it, in the magnetic field
  2. It turns because current works in opposite directions on opposite sides of the coil causing a force in opposite directions and it to turnIncreasing the turning affect :Ensures that direction of current switches every half turn
  3. Increasing number of turns on the coil
  4. Using a stronger magnetic field
  5. Increasing current
• Loud speakers

  How to change pitch

  • Coil attached to a cone in a magnetic field
  • When alternating current flows through the coil
  • It pushes the cone forwards and backwards creating a noise
  • To change pitch(frequency) change the frequency of the alternating current used
• Force on Charged particles

  Moving charged particles are current

  A force is exerted on them as long as they are not moving parallel to the field
• Electromagnetic induction

  Generator effect

  Increasing induced voltage

  When a conducting wire cuts a magnetic field voltage is induced

  If it is part of a complete circuit current is also induced

  • Move the wire through magnetic field faster
  • Use a stronger magnetic field
  • Increase number of coils
• How is voltage also induced ?

  Voltage can be induced when a coil experiences a changing magnetic field

  The faster the rate at which the magnetic field changes the stronger the voltage
• How can electricity be generated?

  By rotating a magnet within a coil

  As the magnet rotates the coil experiences a changing magnetic field

  Inducing a voltage and therefore a current

  1. Number of turns
  2. Increase strength of magnetic field
  3. Increase speed at which magnet rotates
• Transformer


  Consists of two coils wrapped tightly around a soft iron core
• What a transformer does


  Changes the size of voltage
• How a transformer works

  Alternating voltage in the primary coil produces alternating current which cuts the magnetic field of the secondary coil which produces an alternating voltage in it
• Transformers are 100% efficient
• Power is constant in a 100% efficient transformer, so Primary Voltage and current = Secondary Voltage and current</b>
• Step up transformer


  • Has more turns on the secondary coil than the primary
  • This means the voltage of the secondary is greater then that of the primary
• Step up transformers are used for transmission in power lines which increase voltage and decrease current