back Emf (1 Viewer)

[ANgeLNad]

Hello ..Can anyone explain the Back emf to me in simple words.. coz i cant exactly get it i have read through excel, done the dot point, read through txt book and even read through the OTEN DE learning materials.. which they seems to give good explianations but t this one especially and EDDY CUrrents.I dont seem to understand..
Reply A.S.A.P

 

[Lazarus]

When a conductor is within the vicinity of a changing magnetic field, small circular 'eddy currents' are induced. If the conductor is 'whole' (and not, say, serrated) then the eddy currents will join together to form a larger circular current (or, if serrated, as large a current as possible without it being interrupted). This is the induced current, and it flows in a direction such that the magnetic field it generates will oppose the magnetic field that induced it. This induced current is called the 'back emf'.

Technically, emf (electromotive force) refers to voltage, not current, buuuut they're related anyway and you don't really need to worry about those kind of specifics for the HSC.

 

[1234567]

back emf:

when the motor is running, the coil constantly cuts the magnetic field thus there is a changing magnetic field, by faraday, this cutting flux would induce a current, and by lenz's law, this induced current would oppose the motion of the cause, thus this current is in the opposite direction of the emf input, and so it's called back emf.


eddy current:

still using the idea of lenz's law, when a moving conductor(in this case a piece of metal or watever) is in a magnetic filed, and changing the strength of the magnetic filed, it experiences a force, which also has currents induced in it. in this case the current induced is circular, and the force is trying to act against the motion of the metal piece or something. so u can work out whether the curent is anticlockwose or clockwise using hand rules .

 

[Dumbarse]

they have to be the 2 hardest concepts in motors and generators

 

[ANgeLNad]

true

yeah i guess they are

 

[Halidsadee]

so can we say, :jaw:

Induced current in motor > generates back emf (opposit current)

Induced current in a piece of metal surface > genereates eddy current (circular motion)

 

[1234567]

yeap.
by the way '>' means leads to rather than greater than right?

 

[Halidsadee]

Yeaaaaaaaaaap,
" > " in this state means "leads to"

 

[zemaj]

Just to clarify:

back emf can be thought of as either;
o conservation of energy (Lenz's law)
o a reaction of eddy currents/ induced field

Not too hard... but best answers should explain both IMO.

-zemaj