magnetism and electromagnetism

• like poles will repel
• opposite poles will attract
• forces between the poles of two magnets are a type of non contact force
• magnetic field lines are always closed loops
• a magnet has both north and south pole
• only iron, cobalt and nickel are magnets
• a permanent magent is one with its own magnetic field. The magnetism cannot be turned on or off
• an induced magnet is a material which becomes magnetic only when placed within a magnetic field
• the magnetic field is the area surrounding a magnet where the force is acting on another magnet or magnetic material
• magnetic fields can be observed using a compass
• a magnet always causes a magnetic material to be attracted
• the force is strongest where the lines are closest together and at the poles
• magnetic field lines always come away from the North Pole and towards the South Pole
• the earth produces a magnetic field and a magnetic compass uses this to aid navigation
• a magnetic compass can be used to plot and draw the magnetic field lines around the earth
• a circular magnetic field is produced when a current is passed through a conducting wire. this produces a induced magnet
• strength of a magnetic field can be increased by increasing the current flowing through the wire
• coiling the wire to form a solenoid will also increase the magnetic field strength
• an electromagnet is a solenoid with an iron core
• electromagnets are induced magnets and can be turned on and off
• electric motors, loudspeakers, electric bells, and remotely controlled door locks all use electromagnets
• the motor effect is when a wire carrying current is exposed to the magnetic field of another magnet, then a force is produced on the wire at a right angle to the direction of the magnetic field produced
• flemings left hand rule represents relative orientation of a force produced by the motor effect
• your thumb represents direction of the force
• your index finger represents the direction of the magnetic field
• your middle finger represents the direction of current flowing through the wire
• when the wire carrying the current is coiled, the motor effect acting on it causes the wire to rotate. this is how an electric motor works
• as current flows, the force produced in each side of the coil acts in opposite directions, causing the coil to rotate
• when the coil reaches a vertical position, the force produced is parallel to the magnetic field line and so would be 0, causing the motor to stop rotating
• to maintain rotation of the coil, a split ring communicator is used to supply current to the wire