RealiseNothing
what is that?It is Cowpea
It doesn't.I think Maglev train does use the Meissner effect
It doesn't.I think Maglev train does use the Meissner effect
I talked about back EMF. Not sure if this is right though, but I did a little google search yesterday and the information I found seemed to agree with me. Hoping it's right lol.What was the explanation for the braking of the vehicle from the 'motor acting as a generator'?
Yea i heard from a hsc marker that they only decide marking guidelines and decide what constitutes a good answer after going through lots of papers. Fingers crossed for the photocell but i honestly think we may end up losing at least 3-4 marksThe thing is marking guidelines are actually made AFTER the markers go through a few exams. So they might go through them, see that a large amount of students talked about the solar cell, and it might be accepted in the marking guidelines.
This is what I've been told, fizzy can confirm this or not.
Technically you're right, but that answer style is only taught in Ext. 2 maths, not in physics, so marking people down for writing their answer in m/s would be extremely unfair towards the people not doing ext. 2 maths.BTW. Sorry I haven't read all the replies here but from what I've read it looks like no one has put this answer into units of *rotational* speed (eg radians per second, revs per second, revs per minute etc).
The correct linear speed at the circumference is 51.91 m/s, but shouldn't you divide this by (2 pi r) and give the results in revolutions per second or similar units? Or is circumferential speed considered a good enough answer for "rotational speed" in this course. (This is genuine question BTW, not rhetorical. I'm not doing the course but was helping someone else with it).
Dude, marking guidelines aren't decided upon until AFTER the examination, when they have gone through a few papers (I have never marked HSC, but this is what others have told me!)Well she had a look at the paper months before it was released, and thus knew the marking guidelines beforehand. I called her and she said solar cells are fine to use and I won't get penalised for it
Yes it's definitely related to back EMF. The key thing that they would have wanted here is to recognize the similarity of the DC motor and the DC generator (of course at the level expected here they are identical). So the one machine shifts seamlessly between being a motor and a generator, with the mode of operation depending only upon the relationship between the externally applied voltage and the back EMF.I talked about back EMF. Not sure if this is right though, but I did a little google search yesterday and the information I found seemed to agree with me. Hoping it's right lol.
Now I'm seriously confused. Half say it does, half say it doesn't.It doesn't.
I wrote something like this:Yes it's definitely related to back EMF. The key thing that they would have wanted here is to recognize the similarity of the DC motor and the DC generator (of course at the level expected here they are identical). So the one machine shifts seamlessly between being a motor and a generator, with the mode of operation depending only upon the relationship between the externally applied voltage and the back EMF.
When the externally applied voltage is greater than the internally generated voltage (aka the back EMF) then the direction of current *and power* is into the DC machine, so it operates as a motor. When the applied voltage is less than the back EMF however, then the direction of current and power is reversed, meaning that the machine is operating as a generator.
It would probably also be good to mention that when acting as a generator, that the direction of power is reversed and therefore that the direction of torque at the wheels must also be reverse. Hence the braking effort.
It's like-pole repulsion or something. I'm pretty sure saying Meissner effect is wrong (that's what my teacher told me).Now I'm seriously confused. Half say it does, half say it doesn't.
Isn't it Meissner, but an initial thrust is given, propelling it along the track?
There's EDS and EMS. One doesn't use superconductors, just normal magnetic fields, propelling due to Lenz's Law right?
It levitates due to Meissner, but then the pole repulsion propels it.It's like-pole repulsion or something. I'm pretty sure saying Meissner effect is wrong (that's what my teacher told me).
"In electrodynamic suspension (EDS), both the guideway and the train exert a magnetic field, and the train is levitated by the repulsive and attractive force between these magnetic fields"It levitates due to Meissner, but then the pole repulsion propels it.
Jacaranda said there are two different systems: One that uses superconductors and one that doesn't.
So with EDS, where do the superconductors come into play?"In electrodynamic suspension (EDS), both the guideway and the train exert a magnetic field, and the train is levitated by the repulsive and attractive force between these magnetic fields"
From Wikipedia
Other is EMS which doesn't use superconductors.
And: http://community.boredofstudies.org/showthread.php?t=153723&p=3103543&viewfull=1#post3103543
I guess they create stronger repulsive/attractive forces?So with EDS, where do the superconductors come into play?
You wouldn't lose any marks for mentioning the Meissner effect incorrectlyIt's not like you're going to lose many marks for stating the Meissner effect though, I mean if you included an understanding of superconductor's and their electrical properties, then used Maglev as an example of one, and referenced it's effect on society.. that's most of the question answered. All you've missed is the specific electrical properties of the Maglev train example, not superconductors as a whole, so my bet is that's probably 1 mark lost at best. How many marks was that question worth again?
I'd only lose a mark if I did not have a sufficient reason, but I did have a reason (EDS --> less travel times--> society has more leisure time and can increase living standards efficiently).You wouldn't lose any marks for mentioning the Meissner effect incorrectly
Sounds goodI'd only lose a mark if I did not have a sufficient reason, but I did have a reason (EDS --> less travel times--> society has more leisure time and can increase living standards efficiently).
And it was 7 marks. Should get a 6 at least. Should.
Thanks. I really think that most students actually miss out on band 6's due to their extended response structure, lack of cause, effect, reason for every question and the curveball questions (like the photocell one).Sounds good