Someone explain the graph of induced emf vs time graph please? :) (1 Viewer)

[nerdiichic]

can someone please explain this graph in relation to the revolution of the coil?
because sometimes you are not given the graph of magnetic flux vs time graph in order to work out the induced emf vs time graph.

thank you very much!

 

[Fizzy_Cyst]

can someone please explain this graph in relation to the revolution of the coil?
because sometimes you are not given the graph of magnetic flux vs time graph in order to work out the induced emf vs time graph.

thank you very much!

at (i) Plane of coil is perpendicular to B-field (at this point flux is maximum and induced EMF is zero)
(ii) Plane of coil is parallel to B-field (flux is zero and induced EMF is maximum -- as flux is decreasing, EMF must be positive maximum as E = -n(dBA)/dt)
(iii) Plane of coil perpendicular to B-field (at this point flux is maximum and induced EMF is zero)
(iv) Plane of coil is parallel to B-field (flux is zero and induced EMF is maximum -- as flux is increasing, EMF must be negative maximum as E = -n(dBA)/dt)

Just remember EMF is zero when change in flux is zero (when plane of coil is perpendicular to B-field)
EMF is maximum when change in flux is maximum (when plane of coil is parallel to B-field)

 

[jamesfirst]

Don't you mean EMF is maximum when flux is 0


b) i) Magnetic flux is maximum because you know that Flux = B x A. The perpendicular magnetic field covers the whole area hence the flux is maximum. But the direction of the force is parallel to the direction of the magnetic flux. So using what ever hand rule your teacher told you, my teacher told us to use the Left hand GENERATOR rule, you can determine the direction of the induced current. But since force is parallel to the magnetic field there obviously won't be any induced current.

ii) Using the left hand generator rule: the palm points in direction of the induced force, fingers point in the direction of the magnetic field. Therefore the current will travel from M to N. This is when the flux is minimum since the magnetic field is parallel to the area of the coil.

iii) Magnetic flux is negative because it covers the other side of the area (I think this is the reason why). Negative implies opposite of positive. Same as i) there's no current induced.


Edit: I'm quite confused about iv). The graph says the E is in negative direction however the direction in the plane view is same direction... The graph is showing an AC generator while the drawing is showing a DC generator with split ring commutator ???

 

[nerdiichic]

thanks i understand it now

 

[jamesfirst]

Yeah part iv), I told my teacher and he was confused to...

 

[nerdiichic]

mmm, my teacher is soo crapp! she hardly does anything in class ==;