Electric Motor question (1 Viewer)

[matt_17]

This question was in the trial HSC exam.
It has a diagram of an electrical motor. Therer are 2 magnets (N & S) with a coil in between connected to a split ring touching carbon brushes. The circuit is also attached to a resistor.
What type of current would be produced by the motor?
(A) DC of constant magnitude
(B) DC of varying magnitude
(C) AC
(D) None

Does anyone know the answer? Please post your ideas and I will post back in a couple of days with what I think the answer is and what the (supposedly) correct answer is.

 

[Matthaeus]

My guess is thats its a) its got a split ring commutator so its definitely DC.

Like i want to see what the coil exatly looks like and if theres anything special about the resistor, but my guess is that its a constant resistance resistance meaning that it shouldnt realli make the magnitude of the DC current varying.

 

[wogboy]

It has a diagram of an electrical motor. Therer are 2 magnets (N & S) with a coil in between connected to a split ring touching carbon brushes. The circuit is also attached to a resistor.

Going by that description (without the picture), B is the correct answer since the split ring commutator indicates DC (current always goes in same direction), but there will be points in time (namely when the brushes hit the splits in the commutator) that the current is zero in magnitude. And while the brushes are the furthest away possible from the split in the commutator, the current will be maximum in magnitude.

 

[Matthaeus]

Originally i was divided on a) or b), but im just wondering about what the question means. Cause conventionally when ppl talk about the magnitude of current they mean rms rather than the absolute value sine curve that is DC, and you realli have to look at the coil to see how exactly it would work. Im guessing that the question is focusing on the resistor to throw ppl off.

 

[Xayma]

No it will produce b). The only time what it was connected to would matter would be if it was also connected to a capacitor which will slightly flatten it out, but it will still have a slightly varying magnitude.

 

[chickenntaters]

Do motors produce current? I thought only generators did.

 

[matt_17]

In the exam, I put D - none as, like chickenntaters said, motors don't produce current. But my teacher says the correct answer is B

 

[BlackJack]

With few exceptions, if you turn the electric motors manually you'll get a current flowing. In fact, when you look at all the hsc pics of them you'll find that they look almost exactly identical.