alternating currents

Question 1

define mean power

Answer 1

average power dissipated in the resistor <Pac></Pac>

Question 2

define Irms / Vrms

Answer 2

the value of the direct current or voltage that produces thermal energy at the same rate in a resistor

Question 3

what is a function of a transformer

Answer 3

a device that uses mutual electromagnetic induction to vary (step up/down) an alternating voltage

Question 4

what are the requirements for an ideal transformer

Answer 4

1. no energy loss in coils & core during operation
2. no flux leakage
3. at any instant, magnetic flux through each turn is the same in both primary and secondary coils

Question 5

how does copper wires lose power?

Answer 5

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

Question 6

how to combat heating effect due to eddy currents induced in the iron core?

Answer 6

the iron core is made of laminated sheets, cutting across the path of eddy currents, to increase resistance to current flow

Question 7

how to combat hysteresis loss?

Answer 7

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

Question 8

how to combat magnetic flux leakage?

Answer 8

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

Question 9

define refcitication

Answer 9

conversion of alternating current to direct current by diodes