Motors and Generators Question (1 Viewer)

[Jonothancroller]

So I was doing the 2013 HSC and came across this question.

The answer is B. I'm wondering why there would be no current produced by the generator? Would it not still exert a force on the electrons, thus producing a current? I recognise that eventually a charge would build up and the current would no longer flow, but even in an open circuit would a current not be produced for at least some time by the generator?

 

[pikachu975]

No the switch is open, the circuit is broken and current can't flow. There WILL be emf (voltage) though, just not current.

 

[Jonothancroller]

No the switch is open, the circuit is broken and current can't flow. There WILL be emf (voltage) though, just not current.

How can there be an EMF but no current? Won't the EMF force the electrons to move, hence producing a current? Or is there some technical definition of current that encompasses more than just 'the movement of electrons'?

 

[pikachu975]

How can there be an EMF but no current? Won't the EMF force the electrons to move, hence producing a current? Or is there some technical definition of current that encompasses more than just 'the movement of electrons'?

When the switch is open, there is infinite resistance in the wire and I = V/R and V/infinity is basically 0, so the current is negligible.

There is emf because Emf = -delta flux / delta time according to Faraday, and since you're turning the rotor there is a change in flux over time and hence, an emf is induced.

 

[Jonothancroller]

When the switch is open, there is infinite resistance in the wire and I = V/R and V/infinity is basically 0, so the current is negligible.

There is emf because Emf = -delta flux / delta time according to Faraday, and since you're turning the rotor there is a change in flux over time and hence, an emf is induced.

Okay I think I understand that, thanks.