little help (1 Viewer)

[ashtor]

were doing motors and generators now and it turned out harder than i thought. Just a little question, what exactly is an emf, and how does it produce a current? thnx

 

[smegthehead]

think of an emf as a voltage that is induced when a coil experiences a change of flux. Flux can be described as the amount of magnetic field lines passing through the opening of a coil at a certain time, and is determined by:

flux= magnetic field strength x area of opening of coil x sin theta

note that theta in this instance is the angle between the plane of the coil and the magnetic field lines.

Now that you know what flux is you then use faradays law to find the induced emf (or voltage):

emf= change in flux/change in time

note that time is in seconds, and that the units of emf are volts

how does it produce a current? simple. remember the equation V=RI ? well thats what you use here, just plug your induced voltage in and the resistance of the complete circuit and there you have your current.
hope that was some help matey

 

[smegthehead]

oh yeah did you want me to explain it in terms of a single wire being swept through a magnetic field too?

 

[ashtor]

thanks smeg...explained it better than my teacher.
whats this about a single wire being swept through a magnetic field??

 

[smegthehead]

alrighty, consider the area swept out by a wire in a certain time (t). The area that is swept out is given by:

Area = length x velocity x time

so therefore the amount of flux that is swept through the wire is

flux = Blvt (field strength x length x velocity x time)

after that you just use faradays law as described above to get your emf

NOTE: if you put flux= Blvt into faradays equation, you end up getting
emf = Blvt/t = Blv
this is basically the only equation you use when straight wires are being dragged across a magnetic field perpendicular to the field lines. When the conductor is being dragged through at an angle, use emf= Blv x sin theta (although it isn't very likely they'll give you a question on it)

sorry if that was a bit confusing, if you need for me to clarify anything just yell

 

[ashtor]

beudaful...thanks

 

[beverly]

can someone tell me what is exactly meant by 'external' magnetic field, as compared to just a magnetic field?

 

[Xayma]

External magnetic field is used to avoid confusion. As a current-carrying conductor generates its own magnetic field it helps to avoid confusion.

 

[beverly]

ahhh...got it. thanks

 

[za]

lak yahhssaaaaaaaaaaan

 

[ashtor]

wlek yahamzehhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh:jaw:

 

[blackbunny]

how about some help with force between two parallel current carryning wire check that topic out

 

[The Bograt]

is there a difference between induced current and induced voltage? Cause I know a bit about the induced current and the only thing with the voltage ive done is a demo with an inductor coil.

 

[Rahul]

use the right hand screw rule to find the direction of mag field in each wire and then use mag rule [opposite charges attract, similar charges repel] to find the activity in the place where the two mag fields cut.