Magnets and Motors

• Magnetic material eg

  Iron and Steel
• Electromagnet is made by wrapping wire around an iron core.
• Law of Magnetic Poles
• Hard magnetic material can become a permanent magnet eg steel


  Soft magnetic material can form temporary magnets eg Iron
• Induced Magnetism can be created using: Contact method, Stroking method and electrical Method
• Contact Method only suitable for creating Temporary

  magnets
• Stroking method to make a permanent magnets, therefor must use steel
• Electrical method must use DC current and must place a long coil of wire surrounding a piece of iron or steel
• Destroying Magnism: Hammering, Heating and passing AC current in a coil of wire surrounding the magnet
• Magnetic field: the space surrouding the maget in which a magnet can produce a magnetic force
• Magnetic field always pont from magnetic north (Geographical south) to magnetic south pole (Geographic north). Therefore plotting compass always pointed to Geographic north
• Iron filings and plotting compass are used to observe magnetic field paterns
• Straight wire has a circular magnetic field
• Right hand grip rule to find direction of magnetic field lines around a wire carrying a current. Thumb point to direction of current and fingers point to direction of magnetic field lines
• Solenoid: A long coil of wire. The direction of the magnetic field inside a solenoid is opposite that of the outside
• strength can be varied: by increasing number of turns, increasing the current and adding an iron core in its centre
• Use right-hand grip rule to find the direction of magnetic field lines in a solenoid: To do so we must first find the north and south poles of the solenoid. 1)Fingers point to the direction of magnetic field lines. 2) Thumb points to north. And then just remember that magnetic field lines are always from north to south
• Electromagnets are used in microphones, loudspeakers, electric bells, scrapyards
• We use conventional current: + to -
• The motor effect/Catapult effect is when a wire carrying a current is placed in a magnetic field and a force is produced. To determine the direction of the force we use Flemings Left Hamd Rule: 1)Motion of wire (malta) 2)Force- magnetic therefore from north pole of magnet to south pole(football) 3)Current- direction (club)
• If a wire is PARALLEL to the magnetic field then no force is applied
• Electric motor. A machine that converts electrical energy into mechanical energy. If current provided is DC then a commutator must be used to change direction of current every half turn
• Flux is how many magnetic field lines pass through an area at one time
• Faraday's Law states that the current induced in a conductor is directly proportional to the rate of cutting of flux.

  size of current induced depends on

  1. speed of wire cutting magnetic field
  2. strength of field
  3. length of conductor in the field
• Lenz Law: The direction of the induced current always opposes the change producing it
• Iron core transformer: to change voltage from a source into another voltage. P input = P output!

  Primary/input coil & Secondary/output coil

  Iron core strenghtens the magnetic field of the primary coil
• How iron cored transformer works:

  1. The input current starts to flow in the primary coil
  2. A magnetic field is generated around the primary coil
  3. The field lines reach the secondary coil and curing of flux occurs, since current is AC.
  4. An induced current is generated in the secondary coil(Faraday's Law)