magnetism and electromagnetism

• direction of magnetic field

  from the north pole to the south pole
• right-hand grip rule

  if the end of the coil looks like it flows anti-clockwise it's North, if it's clockwise it's South
• what is the motor effect?

  when a current flows in an external magnetic field it experiences a force, since the magnetic field around the current interacts with the external magnetic field
• how can magnetic field strength be increased?

  move the poles closer together, use stronger magnets
• loud speaker explanation

  when current flows through the coil it creates a magnetic field around the coil, the magnetic field from the coil interacts with the magnetic field of the permanent magnet, producing a force on the coil, when the ac current in the coil changes direction it reverses the direction of the force, causing the coil to oscillate, in a loudspeaker this causes the oscillations produce soundwaves
• transformer equation


  vp/vs = np/ns
• power equation

  eff x ip x vp = is x vs
• primary transformer

  vp causes ip which produces bp
• secondary transformer

  bs induces vs which causes is
• Step-up transformer

  has more coils on the secondary, so potential difference increases
• step-down transformer

  has more coils on the primary, so potential difference decreases
• step-up transformer explanation

  an alternating potential difference in the primary causes an alternating current in the primary which produces a changing magnetic field. The iron core guides the magnetic field around the transformer so the magnetic field changes around the secondary coil. A potential difference is induced across the ends of the secondary. If the secondary is part of a complete circuit, a current is induced in the transformer.
• what is a dynamo?

  a DC generator
• what is an alternator?

  an AC generator
• what is a split ring for?

  a dynamo
• what is a slip ring for?

  an alternator
• what is the generator effect?

  the magnetic field changes around a conductor or the conductor moves relative to a magnetic field. A potential difference is induced across the ends of the conductor. If the conductor is part of a complete circuit a current is induced in the conductor.
• what does the size of the force in the motor effect depend on?

  size of the current and strength of the magnetic field
• what are slip/split rings for?

  they prevent the wires tangling
• what are brushes for in a generator?

  maintaining electrical contact
• how is an ac potential difference induced in an alternator?

  side A move up throught the magnetic field and then moves down, so the direction of current is changing, creating an alternating current
• how can the size of the induced potential difference in a generator be increased?

  adding more turns to the coil, using a coil with a larger cross-sectional area, using a stronger magnetic field
• frequency of the induced current in a generator

  frequency is equal to the number of rotations of the coil per second
• when is no potential difference induced in an alternator?

  when the coil is vertical as the sides of the coil are moving parallel to the magnetic field
• what happens if you turn the handle of the generator quickly?

  there is a high amplitude and frequency, but low time period
• similarities of an alternator and dynamo

  both contain a coil which is spun, contain permanent magnets to provide a magentic field, contain brushes, use a conductor moving through a magnetic field to induce a potential difference across the coil
• differences between an alternator and dynamo

  ac potential difference and dc potential difference. slip ring and split ring commutators. in an alternator the slip rings are always connected to the same side, but in a dynamo the commutator reverses which side of the coil is connected to a particular brush.