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Motors and Generators

Motors and Generators. Physics 12 Adv. Comprehension Check.

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Motors and Generators

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  1. Motors and Generators Physics 12 Adv

  2. Comprehension Check • A coil that consists of 500 turns has an edge 15cm long that carries a current of 1.0A to the right. If the edge of the coil is inside a magnetic field of 0.20T pointing out of the page , what is the force the field exerts on the coil? • The magnetic field of the Earth is 0.030mT and is approximately horizontal in the room (pointing south). A 1.0m horizontal wire experiences a .15mN force toward the floor. What is the current in the wire? (Bonus – what is the orientation of the wire and which way is the current flowing)

  3. Comprehension Check • 15N • 5.0A, wire runs east-west and current is flowing to the west

  4. DC Electric Motor • If a current carrying coil is placed in a magnetic field, it will experience torque • This will cause it to rotate so that it no longer experiences a force that causes it to rotate • At this point, a split ring commutator will reverse the current direction so that the coil will continue to rotate

  5. AC Electric Motor • The design of the AC motor is similar to the DC motor except the split-ring commutator is replaced by two slip-ring commutators • As AC current is alternating, the voltage source will reverse the current in the loop so the split-ring commutator is no longer required

  6. DC Motor – Step by Step

  7. Motor Questions • How could you increase or decrease the frequency of rotation of a motor? • How could you increase the rate of energy output for a given motor (assuming no changes in the actual construction)?

  8. Lenz’s Law • When a conductor interacts with a magnetic field, there must be an induced current that opposes the interaction, because of the law of conservation of energy

  9. Eddy Currents • These are an application of Lenz’s law and can be used in balances in order decrease the time it takes to come to rest

  10. Generator Effect • With a motor, a moving charge in a magnetic field results in a force on the wire • In a similar manner, moving a magnet past a conducting wire will result in a force on the charge carriers (i.e. a current)

  11. The fingers point in the direction of the magnetic field The thumb points in the direction of motion of the wire The palm shows the direction of the emf (electromotive force) Right Hand Rule for Generator Effect

  12. A DC generator is essentially a DC motor that is designed to convert motion to electricity instead of vice versa The voltage will alternate between a max and zero DC Generator

  13. The difference with an AC generator is that in does not require a split-ring commutator but instead uses two slip-ring commuators This is because the direction of current in an AC device alternates (positive/negative) AC Generator

  14. Electromotive Force • The emf is a function of: • Magnetic Field (B) • Length of wire (L) • Speed of wire (v)

  15. Section Review • Page 796 • 1-7

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