Magnetism and Electro-magnetism

• How a Transformer Works:

  -Apply an alternating current across the primary coil

  -This produces an alternating current through the primary coil

  -This produces an alternating magnetic field inside the iron core

  -Because the current is alternating, the field changes direction regularly

  -This field cuts the secondary coil

  -Thus an alternating potential difference is induced across the secondary coil, which creates an alternating current
• The Speaker

  -A current induces a magnetic field in the coil

  -The magnetic field interacts with the permanent magnet

  -Thus, the coil moves, which is attached to the speaker cone

  -As the cone moves, it produces a sound wave

  -An A.C. is required to reverse the current flow and make the speaker oscillate

  -The frequency of the A.C. determines the frequency of oscillation and hence the pitch of the sound
• The Microphone

  -The soundwave causes the diaphragm to vibrate

  -This causes the coil to move back and forth

  -The coil cuts the magnetic field lines

  -This induces a potential difference

  -Since the coil moves backwards and forwards an alternating current is produced
• The Dynamo (Motor)

  -The current flows from the positive terminal around the coil of the wire

  -The motor effect means that part of the coil experiences a downwards force, and part of the coil experiences an upwards force

  -This the coil of the wire rotates

  -The split ring commutator swaps the positive and negative connections every half turn

  -Thus the current swaps direction every half turn

  -Hence the forces acting on the coil will always be in the same direction

  -Which means the coil will continue to rotate
• This is the graph of a Dynamo

  
• This is the graph of an Alternator

  
• The four ways to increase the strength of a solenoid are:

  -increase coil density

  -increase the current

  -increase the number of coils

  -introduce an iron core to create an electro-magnet
• When a magnetic field interacts with a magnetic material, an induced magnet is created
• The four magnetic materials are:

  -Iron

  -Nickel

  -Cobalt

  -Steel
• A Step-Up transformer has a larger potential difference in the secondary coil than the primary coil
• A Step-Down Transformer has a higher potential difference in the primary coil than the secondary coil
• A solenoid enhances the magnetic field around a wire as coiling the wire causes the fields to align and form a giant magnetic field, rather than having lots of them perpendicular to the direction of current
• Dynamo (Generator)

  -The coil moves through the magnetic field

  -So a potential difference is induced

  -There is a complete circuit so a current is induced

  -Each half revolution the two halves of the commutator switch brushes

  -So the direction of the induced current does not reverse every half revolution