Magnetism and Electromagnetism

• Magnetic Field - A region where permanent magnets, magnetic materials and current - carrying wires experience a force
• Magnetic material - A material that can become an induced magnet if in the field of a permanent magnetic field.
• Permanent Magnet - A magnet that has a constant magnetic field surrounding itself
• Field Lines show:

  1. where the magnetic field is
  2. North away South towards
• Where is the magnetic field around a bar magnet strongest:

  Where the lines are closest together.
• 3 magnetic elements:

  Iron, Nickel and Cobalt

  A Common magnetic alloy is Steel

  2 metals that are non magnetic are Silver and Gold
• If a material is magnetically hard it means that it retains its magnetism for longer after removed from the permanent magnet.

  If a material is soft is retains its magnetism for a short time.
• Current downwards into the sheet provides clockwise field lines with each having arrows, each getting further apart from each other and having 3 with an x in the center.
• A current outwards of the sheet provides anticlockwise field lines with each having arrows, each getting further apart from each other and having 3 total rings with a dot in the center.
• Around a solenoid has a coil with uniformed field lines running through the coil which are equal spaced and not overlapping. The current goes from N to S and also has field lines in a loop around the sides of the solenoid.
• To increase the strength of the magnetic field around the current of a straight wire you will need to increase the current.

  To change the direction of the magnetic field you will need to reverse the current.
• TO increase the strength of the magnetic field around a solenoid you can introduce an iron core, increase the current flowing through the wire or increase the turns on the coil
• Catapult field - when the arrows point the same direction is the strongest
• FLEMMING'S LEFT HAND RULE - Thumb shows the direction of the force exerted, 1st finger shows the field the N to S. 3rd finger shows the current of the wire positive to negative.

  All have to be 90 degrees from eachother
• To increase the size of the force you should apply a stronger magnetic field, a bigger current and a longer wire.
• When the switch is closed a conventional current will flow around the circuit an through the coil in an anticlockwise direction .The magnetic field acts from north to south. The right arm of the wire will experience a force down based on Flemming's Left Hand rule. The left arm of the coil will move up, so the coil will rotate in a clockwise direction due to the momentum of the coil. Every half turn the split ring commutator reverses the current.
• If you add more coils of wire the speed of the motor will increase

  If you reverse the current you will reverse the direction of the spinning coil

  If you use weaker magnets it will decrease the speed of the motor

  If you use fewer coils of wire you will decrease the speed of the motor

  If you increase the current you will increase the speed of the motor

  If you swap the magnets over you will reverse the current.
• LOUDSPEAKER

  1. An alternating current passes through the coil
  2. It produces a magnetic field around the coil
  3. The magnetic field interacts with the permanent magnetic field causing a force on the coil
  4. Reversing the current changes direction of the force
  5. The coil will vibrate and cause the cone to vibrate
  6. This vibrates the air which is a sound wave
• Iron rods in a solenoid will repel if magnetized as they will be temporarily magnetized with the same polarity because it is a magnetic material.