magnetism and electromagnetism

• the magnetic forces are strongest at the poles of a magnet
• when we bring two magnets close together than they exert a force
• two like poles repel
• two different poles attract each other
• permanent magnet produces its own magnetic field eg a bar magnet
• induced magnet an object that becomes a magnet when it is placed in a magnetic field
• induced magnet always causes a force of attraction
• if we take away the permanent magnet than the induced magnets will lose most or all of their magnetism quickly
• magnetic material:

  • iron
  • steel (alloy of iron)
  • cobalt
  • nickle
• magnetic material can be made into a permanent magnet or induced magnet
• if we place a magnetic material into a magnetic field, the material will experience a force of attraction
• magnetic field: a region around a magnet where a force acts on another magnet or on a magnetic material
• if you place a magnetic material into a magnetic field the magnetic material becomes an induced magnet now attracted to the permanent magnet
• the strength of the magnetic material field depends on the distance from the magnet
• the direction of a magnetic field can be found using a compass
• a magnetic compass contains a small bar magnet
• if we plac ea compass near a bar magnet then we can plot the magnetic field
• direction runs from north to south
• where lines are close together shows where the field is strongest
• strongest part of the field is at the poles of the magnet
• if we hold the compass away from any magnet then the needle aways points in the north-south direction. this tells us that the earth has a magnetic force
• the earths magnetic filed is due to the earths core
• when a current flows through a conducting wire a magnetic field is produced around the wire
• when the current is turned off then then the compass needle lines up with the earths magnetic field
• when we turn the current on then the compass needle deflects this proves there is a magnetic field around the wire
• the strength of the magnetic field depends on the size of the current
• a larger current produces a stronger magnetic field
• the magnetic field is also strongest closer to the wire
• move futher from the wire the strength of the magnetic field decreases
• if we change the direction of the current then we change the direction of the magnetic field
• a compass placed near this wire would deflect in the opposite direction than before
• we place our right hand so that the thumb is pointing in the direction of the conventional current and so now are fingers are pointing in the direction of the magnetic field
• solenoid: a coil of wire that produces a magnetic field around it
• one way to increase the strength of the magnetic field is to coil the wire more tightly
• when we turn on the current we get a strong and uniform magnetic field inside the solenoid
• ways to increase the magnetic field produced by a solenoid:

  • increase current
  • increase the number of turns of the coil
  • place a piece of iron inside the solenoid
• a solenoid containing an iron core is called an electromagnetic
• an electromagnetic is extremely useful as we can change the strength of the magnetic field by changing the size of the current
• an electromagnetic device is a solenoid containing an iron core
• relay: contains two separate circuits