Motors/Generators (1 Viewer)

[samuelclarke]

Could someone explain why the answer is not A but B. Thanks!

 

[Kimyia]

Its got slip rings so its definitely AC not DC but I'm not sure that its any of the answers. Someone correct me if I'm wrong, but doesn't it start cutting the maximum flux so it shouldn't it be starting with max emf and so be a cos wave not a sine wave?

 

[J-Wang]

Its got slip rings so its definitely AC not DC but I'm not sure that its any of the answers. Someone correct me if I'm wrong, but doesn't it start cutting the maximum flux so it shouldn't it be starting with max emf and so be a cos wave not a sine wave?

no, because it starts initially perpendicular to the magnetic field

 

[deswa4]

Its got slip rings so its definitely AC not DC but I'm not sure that its any of the answers. Someone correct me if I'm wrong, but doesn't it start cutting the maximum flux so it shouldn't it be starting with max emf and so be a cos wave not a sine wave?

The graph of flux will start at maximum (ie a cos wave [can be cos or -cos]) due to its initial position in the field. To calculate EMF we use EMF = - N d(phi)/dt, so it is the negative derivative of the flux graph. This will result in either a sin or a -sin graph for EMF. I'm not sure how to determine whether the flux graph is a cos or a -cos graph.

 

[someth1ng]

This is the shittest question that I have ever seen. What up the the "up" and "down"...

From the diagram, it looks like it starts when the plane of the coil is parallel to the magnetic flux and hence, when change of flux is maximum. This means that it should be none of these graphs.

Whether it is positive or negative depends on the way you connect it to a voltmeter but essentially, both A and B are the most correct.

 

[kiinto]

This is the shittest question that I have ever seen.

+1

At first I thought there may have been a special way to connect the slip rings to an external circuit, that I hadn't been taught, but I searched around and found zilch. It's dependant on how you connect it to an ammeter. Careful you do not confuse "current" and EMF.

Where was this question even?

 

[deswa4]

This is the shittest question that I have ever seen. What up the the "up" and "down"...

From the diagram, it looks like it starts when the plane of the coil is parallel to the magnetic flux and hence, when change of flux is maximum. This means that it should be none of these graphs.

Whether it is positive or negative depends on the way you connect it to a voltmeter but essentially, both A and B are the most correct.

The flux is initially maximum, but the graphs represent current and time, not flux.