Electromagnetism

• Electromagnets are a solenoid with an iron core
• Magnetic materials include: Iron, Nickel, Cobalt, and Steel
• steel is magnetically hard
• iron is magnetically soft
• magnetic poles are the part that exerts the greatest force
• Magnets suspended have been orientated by the earth's magnetic field.
• What is the magnetic field?

  The volume of space where magnetic force is exerted
• denser lines means stronger magnetic force
• what is a uniform magnetic field?

  a field wherein constant force is exerted over a region.
• Uniform magnetic fields can almost be found between a north and south pole.
• Earth's magnetic field:

  • similar to that of a bar magnet
  • caused by electric current through molten core
• south pole = northern greenland
• Induced magnetism is when you place something magnetic in a magnetic field. Hard magnetic materials will retain the magnetism.
• Earth has magnetized some rocks like lodestone.
• Straight wire magnetic pattern is concentric circles. Use the right hand rule to find either the direction of current or force.
• flat circular coil has a line in the middle and circular lines with force pointing away from line in the middle.
• solenoid is a coil of wire carrying an electric current and it looks similar to bear magnet. similar but not identical to a bar magnet
• solenoid magnetic field

  
• Electric bell steps:

  1. Push switch closed
  2. Current flows, electromagnet activated
  3. Soft iron armature is pulled towards the electromagnet
  4. Hammer hits gong
  5. Contact switch opens, cutting electric current
  6. Spring pulls armature back, closing contact switch

  
• Electric bell parts, fill in the blanks:

  A) Switch

  B) Electromagnet

  C) Battery

  D) Spring

  E) Soft iron armature

  F) Hammer

  G) Gong

  
• Relay switch steps:

  1. When switch A is closed, the small current provided by the cell causes the electromagnet to become magnetised
  2. Iron armature is then attracted to electromagnet -> springy contact switch B closes the high voltage circuit
• What is a relay switch?

  A way of using low voltage circuit to switch a high voltage switch remotely.
• Circuit breaker steps:

  1. Current flows from terminal A to B --> through contact and electromagnet
  2. Electromagnet strength increases
  3. Spring 1 pulls apart contact stopping current flow
  4. Reset button pulls contact into original position

  
• How do electrical charges interact with magnetic field lines they AREN'T parallel to?

  Electric charges can be deflected by magnetic fields so long as they aren't parallel to the field lines. Positive and Negative is deflected in different directions.
• The motor effect is when a current carrying wire is placed inside a magnetic field, it will experience/undergo a force provided that the conductor is not placed parallel to the field lines.
• Electric motor steps:

  1. Electric current flows throughout the coil of the electric motor _> it produces oppositely directed forces on each side of the coil
  2. those make it rotate
  3. every half revolution the split ring commutator causes the current in the coil to reverse otherwise the coil would stop in the vertical position
• The split ring commutator specifically:

  • Contact with the split ring commutator through the contact brushes keep the circuit closed.
  • In vertical position the circuit is therefore open BUT momentum keeps it rotating.
  • As it regains contact, current flows in the opposite direction.
• Loudspeaker parts:

  A) Magnet

  B) Speaker Cone

  C) Diaphgram

  D) Coil

  
• How do loudspeakers work?

  • Alternating current from amplifier is what the sound signal consists of.
  • Current flows through the coil of the loudspeaker
  • Because of the motor effect: magnetic field around coil vibrates in step with alternating current
  • coil --> cone vibrates in step with the original sound signal.