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[untouchablecuz]

Im very confused about the graohs of emf versus the angle etc.

So far what I have in my notes is:

AC

Þ[FONT=&quot] [/FONT]EMF: when the angle between the coil and magnetic field is 0 (parallel), the change in magnetic flux is equal to zero. When the angle is 90, the change in magnetic flux is maximum. Since this is AC, the direction changes, signified by the negative values for EMF. Thus, you have a sine graph.

Þ[FONT=&quot] [/FONT]Torque: when the angle between the coil and magnetic field is 0 (parallel), the distance between the coil and axle of rotation is maximum, therefore torque is maximum (T = Fd). When the angel is 90, torque is 0 since d is 0. Thus, you have a cosine graph.

Þ[FONT=&quot] [/FONT]Magnetic flux density: assuming that the magnetic field is uniform, the magnetic flux will be constant; therefore the graph will be a straight line.

Þ[FONT=&quot] [/FONT]Current: from the formula for torque, we can see that torque is proportional to the current. It thus follows that the current will vary as with the torque, following a cosine graph.

DC

Þ[FONT=&quot] [/FONT]The same thing except all the negative values for emf etc are mirrored about the x axis.


Am I correct?

 

[k02033]

 

[k02033]

first notice that the area for which flux passes through is a function of theta

ie











where w is angular frequency of the generator (w=2*pi*f, where f is how many rotations the generator makes in 1sec, so this w guy is controlled by how fast we spin the genertor )

everything in that equation is constant at a set generator speed, except for theta. so just plot emf against theta

 

[k02033]

so rate of change of flux is BAw, ie max at theta =0, haha im little tired, i will read through the rest of your post later..

 

[untouchablecuz]

first notice that the area for which flux passes through is a function of theta

ie











where w is angular frequency of the generator (w=2*pi*f, where f is how many rotations the generator makes in 1sec, so this w guy is controlled by how fast we spin the genertor )

everything in that equation is constant at a set generator speed, except for theta. so just plot emf against theta

Hmmm. The thing is, I did exactly what you have done here but I was under the assumption (from textbooks) that magnetic flux varies according to the cosine of theta (if B and A are constant). I.e. mag. flux = BAcos(theta)

Btw, thanks for the help.

 

[k02033]

which textbooks?

 

[untouchablecuz]

excel (new one)
surfing physics (i think it was this one)

being a function of the sine of theta makes more sense

 

[untouchablecuz]

usually A is defined to be a vector perpendicular to the plane giving a cos factor

A is vector quantity? :S

Ok, so wat does Ø equal: BAsin(theta) or BAcos(theta)

 

[k02033]

yea hsc doesnt use the angle between the normal and B field, hsc uses orientation angle

orientation angle is the theta in my 1st diagram

the angle between the normal and B field is

 

[k02033]

so if you want to use the angle between the normal and B field
then