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electromagnets

electromagnets. FLHR the m otor effect. Last lesson:. Magnetic materials Shape of magnetic field around a bar magnet Shape of magnetic field around 2 similar/opposite poles Magnetic field due to a straight current-carrying conductor

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electromagnets

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  1. electromagnets FLHR the motor effect

  2. Last lesson: • Magnetic materials • Shape of magnetic field around a bar magnet • Shape of magnetic field around 2 similar/opposite poles • Magnetic field due to a straight current-carrying conductor • Magnetic field due to a loop of current-carrying conductor • didn’t really get to Magnetic field due to a solenoid

  3. Magnetic field around a solenoid A what ???? OK. Consider the magnetic field around one loop. Now multiply that along the whole length of the solenoid

  4. Magnetic field around a solenoid Looks just like a bar magnet So which end is the north pole? Which end is the south pole? How can I remember that?

  5. OK… moving on • So we know about the magnetic fields from magnets and the magnetic fields due to currents… • What happens when we put them together? • Watch this demo:

  6. The motor effect • What do you think the factors are that can affect the size of the force? • Observe that the direction of the force can also be changed • We use Flemings' Left Hand Rule to remember this

  7. Fleming’s Left Hand Rule

  8. The wire will move… downwards

  9. The wire will move….. “out of the board” or towards you

  10. Which is the North pole? The bottom one

  11. The motor effect N • Why? • Draw the field-lines for the last example. • Start with the fixed magnets Now add in the magnetic field around the wire LINES CANNOT CROSS THEY CAN CANCEL OUT S

  12. Much better diagrams :)

  13. One step harder….

  14. Electric motor • List 5 objects which use an electric motor • BUT how do we stop the wire getting tangled up or ‘flip-flopping through just 180 degrees and then back again? HOMEWORK • Search for an image of a simple electric motor which includes ‘brushes’ and a commutator’. • Explain the role of the brushes and the commutator

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