Ch21 Electromagnetic Induction Flashcards
Define induced e.m.f./ induced voltage:
The e.m.f. created in a conductor when it cuts through magnetic field lines
Define electromagnetic induction:
The production of an e.m.f
across an electrical conductor
when there is relative movement
between the conductor and a magnetic field
Define Flemings right-hand rule:
A rule that gives the relationship
between the directions of force, field and current
when a current flows across a magnetic field
Define a.c. generator:
A device such as a dynamo
used to generate alternating current
Define slip rings:
A device used to allow current to flow to and from the coil of an a.c. generator
Define Lenz’s law:
The direction of an induced current
always opposes the change in the circuit/the magnetic field
that produces it
Define power lines:
Cables used to carry electricity from power stations to consumers
Define national grid:
The system of powerlines, pylons and transformers used to carry electricity around the country
Define transformer:
A device used to change voltage of an a.c. electricity supply
Define primary coil:
The input coil of a transformer
Define secondary coil:
The output coil of a transformer
Define step-up transformer:
A transformer which increases the voltage of an a.c. supply
Define step-down transformer:
Transformer which decreases the voltage of an a.c. supply
What is the transformer equation?
Voltage across primary coil/voltage across secondary coil = number of turns on primary/number of turns on secondary
Vp/Vs = Np/Ns
What is the equation for power loss?
Power loss = square of current in the cable x resistance
P = I²R
Assume that there is no power lost in the transformer, what is the equation that links the primary and secondary voltage to the primary and secondary currents?
Power in to primary coil = power out of secondary coil
Ip x Vp = Is x Vs
