generators & dynamos

• The generator effect can be used to:

  • Generate a.c in an generator
  • Generate d.c in a dynamo
• When we say the changing magnetic field induces a current in the coil, we're referring to the fact that the existing current in the coil (which is part of the circuit) changes in response to the changing magnetic field. This change in current is what is induced by the magnetic field.
• ALTERNATOR - type of generator that converts mechanical energy to electrical energy in the form of alternating current

  • A rectangular coil that is forced to spin in a uniform magnetic field
  • The coil is connected to a centre-reading meter by metal brushes that press on two commutator rings
  • they provide a continuous connection between the coil and the meter
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  A) rotation

  B) brushes

  C) alternating

  D) potential difference

  E) meter pointer

  
• When the coil turns in one direction:

  • The pointer defects first one way, then opposite

  1. bc the coil cuts through the magnetic field lines n a pd, and therefore current is induced in the coil

  • The pointer deflects in both directions bc the current in the circuit repeatedly changes direction as coil spins

  1. bc the induced pd in coil repeatedly changes direction
  2. This continues on as long as the coil keeps turning in the same direction

  • The induced pd and current alternate bc they repeatedly change direction

  
• 1. DC Generator:

  • split-ring commutator: convert ac generated in coil to dc.
  • it commutator changes direction of current in coil every half turn, so it flows in the same direction in the external circuit.

  1. AC Generator:

  • no split-ring commutator bc it generates ac directly.
  • slip rings: transfer ac frm rotating coil to external circuit without changing direction.
  • Slip rings allow ac to flow smoothly to load w/o switching directions like DC generator

  1. DC: the split-ring commutator converts AC to DC.
  2. AC: slip rings transmit the AC current without changing its direction.
• DYNAMO - dc generator

  • same as an alternator but has 1 split ring commutator instead of 2 separate slip rings
  • As the coil rotates, it cuts through the field lines
  • This induces a potential difference between the end of the coil
  • AC current varies from zero to a maximum value twice each cycle ofrotation, and never changes polarity(positive to negative) This means the current is always positive (or always negative)
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  A) dynamo

  
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  A) dc

  B) positive

  
• A dynamo typically produces direct current (DC), which means the flow of electric charge is in one direction only, typically from positive to negative. This is because the dynamo uses a split-ring commutator, which ensures that the current flows in the same direction in the external circuit regardless of the rotation of the coil. As a result, the output of a dynamo is typically positive current.
• BICYCLE DYNAMO

  • supply electricity to bicycle lights while in motion
  • a rotating magnet placed inside / next to a coil
  • The magnet is rotated by its connection to the bicycle inside the coil aka the friction wheel and the axle / spindle
  • The magnetic field lines cut thru the sides of the coil - induces a potential difference in the coil
  • Since the magnetic field is constantly changing direction as it rotates, so does the output potential difference
  • This means the output current is also changing direction
  • Therefore, a bicycle dynamo, unlike a normal dynamo, produces alternating current (a.c)
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  A) lamp

  B) wires

  C) tyre

  D) spindle

  E) coil

  F) magnets

  G) rotating

  H) coil

  I) wheels