Section 1 ELECTROMAGNETIC MACHINES

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  • Section 1
    • Magnetic Fields and Motors
      • Wires carrying current in a magnetic field experience a force
        • Current carrying wire and external magnetic fields interact
          • Causes force on wire
          • If current is parallel to flux lines no force acts
          • Direction of force is perpendic. to current & mag field
            • Direction of force given by LHR
              • Wires carrying current in a magnetic field experience a force
                • Current carrying wire and external magnetic fields interact
                  • Causes force on wire
                  • If current is parallel to flux lines no force acts
                  • Direction of force is perpendic. to current & mag field
                    • Direction of force given by LHR
        • Magnetic field around current carrying wires
          • Direction of mag field given by RHR
        • Magnetic field is region where force is exerted on magnetic materials
          • Represented by field lines
          • Lines go from N to S
          • Mag Field strength represented by how close lines are
        • Size of force: F=BIl
          • B is magnetic field strength
            • Also called flux ddensity
              • 1 tesla = Wb/m^2
                • Size of force: F=BIl
                  • B is magnetic field strength
                    • Also called flux ddensity
                      • 1 tesla = Wb/m^2
                      • Vector quantity
              • Vector quantity
          • Forces on a loop can make a motor
        • Electromag-netic induction
          • Magnetic flux is total no. of field lines
            • Mag field strength = mag flux density (B)
            • Measures strength of mag field per unit area
            • Mag flux = BA
            • Flux linkage = mag flux x N (no. turns on coil)
          • Faraday's Law
            • Induced e.m.f is directly proportional to rate of change of flux linkage
              • E.m.f is gradient
              • Area under gives flux change
          • Changes in mag flux induce electromotive force
            • E.m.f induced wherever there is relative motion between conductor and magnet
            • Either conductor or mag field is still and other is moving
            • E.m.f produced when flux lines are cut
              • Only induces current if circuit is complete
          • Charges accumulate on a conductor through mag field
            • Conducting rod moving through mag field will experience force
              • electrons accumulate at end of rod
            • If rod is part of circuit then current will flow
              • Called electromagnetic induction
            • Induces e.m.f across end of rod (like battery)
          • Lenz's Law
            • Induced e.m.f is always in a direction that will oppose the change it causes
              • Conservation of energy
              • Find diction and current
        • Transformers and Alternators
          • Transformers
            • Work by electroma-gnetic induction
              • Change the size of V for an AC
              • Current flowing in  primary coil produces mag flux
              • Mag field passed through iron core to secondary coil
                • Induces alternating voltage
              • Step-up increase V by + turns on 2nd coil
            • Affected by permeability and conductivity
              • Permeance is amount of flux induced
              • Higher the permeancethe greater the amount of flux flux induced
            • Not 100% efficient
              • Small losses of power in form of heat
                • Heat produced by eddy currents in core
                  • Laminating core with insulation reduces
                • Heat generated by resistancein coils
                  • Thick copper wire used to reduce resistance
            • Part of national gird
              • Electricity is sent round country at lowest current
              • Low current means high voltage
                • Step up transformers for transmission
                  • Step down for domestic use
          • Alternators
            • Generator of A.C.
            • Converts KE to electrical energy
            • Induce current by rotating a coil in a mag field

      Comments

      Callum

      Very Impressive. Thank you for this resource.

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