# Generator help (1 Viewer)

#### Jonothancroller

##### Member
https://prnt.sc/h3cwy7

Can someone explain this? My thoughts were it would be D, as from the right hand rule we get that the current will move from X to Y. Hence, X will be the positive terminal and Y will be the negative terminal, as positives are attracted to negatives. However, am I wrong in that this is different because it does not have a power source? And so the positive terminal will be were the most positive charges are, which will be Y as the positives flow towards Y? That would make sense as the answer is B.

#### Jonothancroller

##### Member
http://prntscr.com/h3cz83

And just for confirmation, it is D because there is no back emf in a generator right? Didn't know if they were just being tricky with wording.

#### jazz519

##### Moderator
Moderator
So consider the right hand side of the coil (the wire bit) since there is no power supply this will mean the current will flow in a direction that produces a force on that right hand wire upwards opposing the downward force due to rotating it due to lenz law

So using right hand palm rule. Palm is facing out of the page, fingers pointing right so current is going anticlockwise. So current goes from y to x so answer is b

#### Jonothancroller

##### Member
http://prntscr.com/h3czlr

Final one. I don't get why it is B. Voltmeters don't work when placed in series? But ammeters and lamps should work, right? So why not C?

Moderator

#### jazz519

##### Moderator
Moderator
A contributes because it ensures the movement of the needle is in constants increments (i.e if it was on a ruler 0.1 amps might be 1cm and 2cm would be 0.2 Amps)

B is referring to the radial magnetic field which ensures the constant torque

D cause torque equation has area term which needs to be constant

#### Jonothancroller

##### Member
So consider the right hand side of the coil (the wire bit) since there is no power supply this will mean the current will flow in a direction that produces a force on that right hand wire upwards opposing the downward force due to rotating it due to lenz law

So using right hand palm rule. Palm is facing out of the page, fingers pointing right so current is going anticlockwise. So current goes from y to x so answer is b
Hmmm, I'm not sure how well I get that. Isn't Lenz's law only applicable for changes in magnetic fields? That's how I learnt it anyway.

And then, if we do that right hand palm rule, we get our thumb pointing downwards, which I'm not really sure how it relates to current going anti-clockwise.

#### jazz519

##### Moderator
Moderator
Hmmm, I'm not sure how well I get that. Isn't Lenz's law only applicable for changes in magnetic fields? That's how I learnt it anyway.

And then, if we do that right hand palm rule, we get our thumb pointing downwards, which I'm not really sure how it relates to current going anti-clockwise.
Lenz law applies here too because there is a change in magnetic flux experienced by the coil since it is rotating
Oh sorry I meant from x to y (working in my head so accidentally wrote that) (it’s negative cause the electrons are being repelled from it and flowing to the positive)

#### Jonothancroller

##### Member
Lenz law applies here too because there is a change in magnetic flux experienced by the coil since it is rotating
Oh sorry I meant from x to y (working in my head so accidentally wrote that) (it’s negative cause the electrons are being repelled from it and flowing to the positive)
Okay cool, I get everything now apart from the last part. When we use the right-hand palm rule, we're considering positive charges rather than electrons (coz HSC likes the 1800's throwback) so would we instead get x to y, but positive charges, and so x is positive? When we use the left-hand palm rule we see that electrons will flow from y to x (which is just also deduced from reversing positive flow current).

#### jazz519

##### Moderator
Moderator
Okay cool, I get everything now apart from the last part. When we use the right-hand palm rule, we're considering positive charges rather than electrons (coz HSC likes the 1800's throwback) so would we instead get x to y, but positive charges, and so x is positive? When we use the left-hand palm rule we see that electrons will flow from y to x (which is just also deduced from reversing positive flow current).
Oh yeah true I think it has something to do with the split ring commutator flippping the current direction in the external circuit for why it’s negative

#### Jonothancroller

##### Member
http://prntscr.com/h3czlr

Final one. I don't get why it is B. Voltmeters don't work when placed in series? But ammeters and lamps should work, right? So why not C?
Wait wait I think I understand this one. So, an emf will still be induced in the circuit due to Faraday's law. Thus, when the voltmeter is placed in series with the circuit, it can detect the voltage of the circuit. However, the voltmeter being in circuit stops the other components (i.e. ammeter and lamp) from working.

Is that correct?

#### Jonothancroller

##### Member
Oh yeah true I think it has something to do with the split ring commutator flippping the current direction in the external circuit for why it’s negative
Do you reckon the answer is wrong then? Because with a commutator in a generator, it should just keep the polarities of X and Y the same constantly rather than changing their polarities, as if they were connect to a slip ring.

#### jazz519

##### Moderator
Moderator
Wait wait I think I understand this one. So, an emf will still be induced in the circuit due to Faraday's law. Thus, when the voltmeter is placed in series with the circuit, it can detect the voltage of the circuit. However, the voltmeter being in circuit stops the other components (i.e. ammeter and lamp) from working.

Is that correct?
Yeah the voltmeter has very high resistance which means that the current will practically be 0

#### jazz519

##### Moderator
Moderator
Do you reckon the answer is wrong then? Because with a commutator in a generator, it should just keep the polarities of X and Y the same constantly rather than changing their polarities, as if they were connect to a slip ring.
Yeah it could be (I'll ask some of my friends what they think)

#### Jonothancroller

##### Member
Yeah it could be (I'll ask some of my friends what they think)
Thank you! You've been very helpful.

#### pikachu975

##### I love trials
Moderator
https://prnt.sc/h3cwy7

Can someone explain this? My thoughts were it would be D, as from the right hand rule we get that the current will move from X to Y. Hence, X will be the positive terminal and Y will be the negative terminal, as positives are attracted to negatives. However, am I wrong in that this is different because it does not have a power source? And so the positive terminal will be were the most positive charges are, which will be Y as the positives flow towards Y? That would make sense as the answer is B.
Basically right hand palm rule shows where positive charges go. Aka the positive charges go to Y which makes Y positively charged so X is negatively charged which is what you said

#### jazz519

##### Moderator
Moderator
Basically right hand palm rule shows where positive charges go. Aka the positive charges go to Y which makes Y positively charged so X is negatively charged which is what you said
lol I think we massively overcomplicated it ahahahaha

#### Jonothancroller

##### Member
Basically right hand palm rule shows where positive charges go. Aka the positive charges go to Y which makes Y positively charged so X is negatively charged which is what you said
Ohhh okay, so in a generator, positive charges don't flow towards the negative terminal, but instead the positive terminal? Makes sense.

#### Jonothancroller

##### Member
lol I think we massively overcomplicated it ahahahaha
It seems we did hahahaha. At least I won't forget this