Flashcards
9.3 Motors & Generators
Cards in this deck (23)
- 1force on a current-carrying conductorF = BIlsintheta
- 2torquethe turning moment of a force
T = Fd
T = nBIAcostheta - 3the motor effecta current-carrying conductor in a magnetic field experiences a force
- 4Faraday's discoverywhen a conductor moves such that it cuts across a magnetic field, a current will flow in the conductor
- 5magnetic fluxthe number of magnetic field lines passing through an imaginary area in a given time
- 6magnetic flux densityamount of magnetic flux per unit area / the strength of the magnetic field B
- 7Lenz's lawthe direction of any induced emf will always be such that it opposes the change that caused it.
when a conductor moves through a magnetic field, current flows in the conductor, inducing a second magnetic field thus producing a force on the conductor - 8DC motorelectrical --> kinetic
split-ring commutator - 9back emf in electric motorsas the rotor rotates, coils of wire are cutting flux, which induces a "back emf" between the ends of the wires. back emf is in the opposite direction and opposes the voltage (Lenz's law)
- 10eddy currentscurrent produced by the back emf of a motor
proportional to the speed of the motor
minimised using a laminated soft iron core (insulating oxide layer disrupts eddy currents) - 11electromagnetic brakingelectromagnets brought close to metal wheels, where eddy currents induced in the wheels create a magnetic field which opposes the field producing it, thus slowing the train/ride
- 12induction cooktopswhen AC passes through the coil under the cooktop, a changing magnetic field is created that induces eddy currents in metal pans. the resistance of metal in saucepan transforms electricity into heat energy, cooking the food.
- 13DC generatormechanical --> electrical
split-ring commutator - 14energy loss in transmission linesmainly due to resistance in transmission lines which converts electrical energy into heat
- 15effect of AC generators on societypositive: E transmitted over long distances with minimal power loss, lowered cost of E, led to development of household appliances
negative: increasing atmospheric pollution which is adverse to health, reliance on crude oil leading to the risk of war - 16effect of AC generators on the environmentpositive: power generation now away from population centres, increased efficiency reduces pollution, technology leading to renewable sources of energy
negative: CO2 emissions resulting from electricity generation, thermal pollution from power stations, health risks - 17AC generatorkinetic --> electrical
slip-ring commutator - 18protection for transmissionshield conductors (intercept lightning strike & divert to earth), insulation chains (join wires to metal tower so tower E can't be conducted to wires), earth cable, metal tower, distance between towers
- 19transformersdevice used to change voltages within a circuit by changing the current. changing AC voltages in the primary coil create flux in the iron core, 'linking' with the secondary coil (which has a changing magnetic field through it) hence inducing voltage.
- 20conservation of energy in transformersVp/Vs = Np/Ns
as the current and magnetic field increase in the primary coil, the current in the secondary coil increases in a direction which produces an opposing magnetic field. when the current in the primary coil is switched off, the current in the secondary coil will increase in an attempt to maintain the field at its last stable level - 21impact of transformers on societybenefits: reduced power loss in transmissions, electricity can meet demands of appliances, fewer transmission lines required
problems: increased demand, automation of industry (loss of jobs), risk of electrocution, dependence on electricity - 22AC electric motorelectrical --> kinetic
no commutator since direction of current reverses 50 times/sec - 23AC induction motorprinciple: a rotating magnetic field will exert a torque on a stationary coil
current induced due to changing magnetic field in the stator; interaction of electric field + magnetic field results in torque
Information
- Description
- Flashcards on 9.3 Motors & Generators, created by Grace Easton on 12/07/2017.
- Created by
- Grace Easton
- Views
- 42
- Tags
- Rating