Generator and Transformer

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Generator and Transformer
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Moving Conductor

• If a straight conductor is moved in a path
  perpendicular to a magnetic field, a current is
  induced in the conductor
• No current flows though since not a loop
• Induced emf
• ? B l v
• l length of conductor
• v velocity of conductor

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Example

• An airplane travels at 1000 km/hr in region where
  the Earths magnetic field in 5.0 x 10-5 T. What
  is the emf induced between the wing tips that are
  70m apart?

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Generators (Dynamo)

• Transforms mechanical energy into electric energy
• Coil of wire spins in the presence of a permanent
  magnetic field
• Induces are current in the coil
• Current produced actually fluctuates as the coils
  position in the field changes
• Produces a current that switches direction every
  half a rotation Called Alternating Current (AC)

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Moving Electricity

• How does electric energy transmit over large
  distances?
• Much less energy is lost when it travels at a
  higher V and lower I

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Transformer

• Device that changes voltages
• Two coils around an iron core
• Current supplied to the primary coil induces a
  current in the secondary coil
• By varying the number of windings in the coils
  you can vary the potentials

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Equation
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Types

• Step-up more windings on the secondary coil
  increases the voltage
• Step-down less windings on the secondary coil
  decreases the voltage
• Transformers work only on AC current. Why?

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Transportation

• Electric energy is stepped up for transmission
  and then stepped down for household use

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Problem 1

• A metal airplane with a wing span of 30m flies
  horizontally at a constant speed of 320 km/h in a
  region where the Earths magnetic field is 5.0 x
  10-5 T. What is the induced emf across its wing
  tips?

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Problem 2

• A 20 cm long metal rod is moving at a speed of 10
  m/s in a magnetic field of 0.30 T. Find
• a) the induced emf in the rod
• b) the current in the rod

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Problem 3

• An ideal transformer steps 8.0 V up to 2000 V,
  and the 4000 turn secondary coil carries a
  current of 2.0 A. Find
• a) the number of turns in the primary
• coil.
• b) the current in the primary coil

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Problem 4

• The primary coil of an ideal transformer has 720
  turns, and the secondary coil has 180 turns. If
  the primary coil carries 15 A at a voltage of 120
  V, for the secondary coil what are the
• a) voltage
• b) current