alternating currents Flashcards
define mean power
average power dissipated in the resistor <Pac></Pac>
define Irms / Vrms
the value of the direct current or voltage that produces thermal energy at the same rate in a resistor
what is a function of a transformer
a device that uses mutual electromagnetic induction to vary (step up/down) an alternating voltage
what are the requirements for an ideal transformer
- no energy loss in coils & core during operation
- no flux leakage
- at any instant, magnetic flux through each turn is the same in both primary and secondary coils
how does copper wires lose power?
joules heating of copper wire
soln:
thick copper wire of low resistance is used, particularly for the coil carrying high current at a low voltage
how to combat heating effect due to eddy currents induced in the iron core?
the iron core is made of laminated sheets, cutting across the path of eddy currents, to increase resistance to current flow
how to combat hysteresis loss?
hysteresis loss: energy is used in the process of magnetising the iron and reversing this magnetisation every time the current reverses, heats up the iron core
soln:
iron core made of soft iron which is easily magnetised and demagnetised by magnetic field of the primary coil
how to combat magnetic flux leakage?
some of the magnetic field lines produced by the primary coil do not link w the secondary coil, reducing the emf induced in the secondary coil
the presence of iron core maximises the flux linkage between the primary and secondary coils
flux leakage can also be minimized by having a good design, in the E-I shaped iron core, the secondary coil is wound on top of the primary coil and the iron core forms a closed loop
define refcitication
conversion of alternating current to direct current by diodes