# 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)
• Induced e.m.f is directly proportional to rate of change of flux linkage
• 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