Electromagnetism + a.c. Flashcards
State Faraday’s Law of Electromagnetic induction
induced e.m.f proportional to rate of change of magnetic flux linkage
State Lenz’s Law
induced e.m.f/ current acts in such a direction to produce effects to oppose the change causing it
What is meant by magnetic field
-region of space where
-a force is experienced by current-carrying conductor/ moving charge/ permanent magnet
Define the tesla
-unit of magnetic flux density/ magnetic field strength
-uniform field normal to wire carrying current of 1A
-giving force per unit length of 1Nm-1
Why the path of the electron in the magnetic field is the arc of a circle
-magnetic force is always normal to velocity/ direction of motion
-magnitude or magnetic force constant
-speed/ kinetic energy is constant
-so provides the centripetal force
With reference to d.c, what is meant by root-mean-square value of an a.c
the value of the direct current producing same mean power/ heating in a resistor
What is meant by root-mean-square (r.m.s) value of an alternating voltage
either the value of steady/ constant voltage that produces same power (in resistor) as the alternating voltage
or
if alternating voltage is squared and averaged, the r.m.s. value is square root of this averaged value
Define magnetic flux density
-force per unit length
-on straight conductor carrying unit current
-normal to the field
State why the transformer has an iron core, rather than having no core
core reduces loss of magnetic flux linkage/ improves flux linkage
Why core is laminated
-reduces size of eddy currents in core
-so heating core is reduced
With reference to the action of a transformer, why the input to the transformer is an alternating voltage, rather than a constant voltage
-alternating voltage give rise to changing magnetic flux in core
-changing flux links the secondary coil
-induced e.m.f. (in secondary) only when flux is changing/ cut
A coil of insulated wire is wound on to a soft-iron core. The core is connected in series with a battery, a switch and an ammeter
Use laws of electromagnetic induction to explain why, when the switch is closed, the current increases gradually to its maximum value
-increasing current causes increasing flux
-increasing flux induces e.m.f in coil
-induced e.m.f. opposes growth of current
