electric motors + loudspeakers

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4 Terms

1
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describe what happens in an electric motor:

  1. forces act on two side arms of coil of wire carrying current

    • one force acts up

    • once force acts down

    • so spindle rotates

  2. split-ring commutator keeps motor rotating the same direction

2
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how can the motor direction be reversed?

  • swap polarity of d.c. supply

    • reverse current

  • swap magnetic poles

    • reverse field

3
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how do loudspeakers and headphones (tiny loudspeakers) work?

  1. alternating current

  2. current in coil creates electromagnetic field

  3. electromagnetic field interacts with permanent magnet generating a force

    • pushes cone out

  4. current flows in opposite direction

  5. electromagnetic field direction reverses

  6. force on cone pulls it back in

  7. alternating current direction causes cone to vibrate

  8. cone vibrations cause pressure variations in air

    • sound waves

4
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what is the frequency of the sound wave?

frequency of a.c.