eddy currents. (1 Viewer)

[RishBonjour]

I'm confused, different sources say different shit.
Do they flow in slotted tubes, but are weak? or are eddy currents completely cut off because of slots?

 

[Sindivyn]

They still flower, just weaker.

 

[RishBonjour]

HSC board of studies 2011 sample answer:
As the magnets fall, they will produce a changing magnetic flux in the walls of both tubes. Lenz’s Law says that this will set up a current (eddy current) that will produce a magnetic field to try to oppose this change. This is possible for the magnet A tube, since the eddy current can flow around the complete circumference. This results in a strong braking force on the magnet. For the slotted tube, the eddy currents cannot flow because the slots break the current path and no braking results. This means that magnet B will fall faster and reach the end of the tube first.

There was also a multiple choice my that had 3 tubes, one slotted, one plastic and one metal. The answer said the plastic and slotted have the magnet fall at the same time...

I learnt is as eddy currents are produced but not as strong, which seems logical.

fucking physics.

 

[Sindivyn]

What you put in bold does make sense though, guess I learnt it wrong. Will have to go over eddy currents again I guess

 

[Beaconite]

they are minimized, therefore less heat loss

 

[nightweaver066]

HSC board of studies 2011 sample answer:
As the magnets fall, they will produce a changing magnetic flux in the walls of both tubes. Lenz’s Law says that this will set up a current (eddy current) that will produce a magnetic field to try to oppose this change. This is possible for the magnet A tube, since the eddy current can flow around the complete circumference. This results in a strong braking force on the magnet. For the slotted tube, the eddy currents cannot flow because the slots break the current path and no braking results. This means that magnet B will fall faster and reach the end of the tube first.

There was also a multiple choice my that had 3 tubes, one slotted, one plastic and one metal. The answer said the plastic and slotted have the magnet fall at the same time...

I learnt is as eddy currents are produced but not as strong, which seems logical.

fucking physics.

I'm going to need to clarify the bolded text with my teacher..

 

[RishBonjour]

Could you guys have a look at this one, from IND 2011.

If the matches light at that position. Shouldn't they reach S at the same time (but reach M differently), considering the speed of light will remain constant and not be effected by the motion of the train?

I don't have a strong grasp on relativity. a tad confused.

The answer says, because P is moving towards S and Q is moving away. if that was the case, shouldn't the light ray from P exceed c?

 

[Beaconite]

it will not be simultaneous to S ...since train is moving right, S will see the light from rear passenger first...because distance from rear passenger and M is decreasing ...

 

[Beaconite]

View attachment 26207

Could you guys have a look at this one, from IND 2011.

If the matches light at that position. Shouldn't they reach S at the same time (but reach M differently), considering the speed of light will remain constant and not be effected by the motion of the train?

I don't have a strong grasp on relativity. a tad confused.

The answer says, because P is moving towards S and Q is moving away. if that was the case, shouldn't the light ray from P exceed c?

You can never exceed c ... it says train is moving at constant speed (inertial frame of reference)

 

[RishBonjour]

You can never exceed c ... it says train is moving at constant speed (inertial frame of reference)

Thats the whole point I am asking about. If S sees them differently, considering they were given off at EQUIDISTANT from S, and SHE/HE was STATIONARY and did not move - it should be simultaneous? whereas M moved towards Q ?

 

[Beaconite]

Thats the whole point I am asking about. If S sees them differently, considering they were given off at EQUIDISTANT from S, and SHE/HE was STATIONARY and did not move - it should be simultaneous? whereas M moved towards Q ?

train is moving, the distance b/w M and two matches stays constant....while for S, the distance changes (train moving away from him)

 

[Parvee]

Thats the whole point I am asking about. If S sees them differently, considering they were given off at EQUIDISTANT from S, and SHE/HE was STATIONARY and did not move - it should be simultaneous? whereas M moved towards Q ?

All you need to say for this question to get full marks is if it is simultaneous or not and why.
So for this my answer would be:
No, S is in a different frame of reference, so what is simultaneous to M may not be simultaneous to S.

 

[RishBonjour]

hmm :/ i guess.
But, just a question, why are the events simultaneous to M? it seems a bit counter intuitive to me considering the diagrams in textbooks. As M is moving towards Q.

Or is it just because the question says so in this paper?

 

[Parvee]

hmm :/ i guess.
But, just a question, why are the events simultaneous to M? it seems a bit counter intuitive to me considering the diagrams in textbooks. As M is moving towards Q.

Or is it just because the question says so in this paper?

Relative to P and Q, M is stationary since they are all inside the train carriage.

 

[asianese]

HSC board of studies 2011 sample answer:
As the magnets fall, they will produce a changing magnetic flux in the walls of both tubes. Lenz’s Law says that this will set up a current (eddy current) that will produce a magnetic field to try to oppose this change. This is possible for the magnet A tube, since the eddy current can flow around the complete circumference. This results in a strong braking force on the magnet. For the slotted tube, the eddy currents cannot flow because the slots break the current path and no braking results. This means that magnet B will fall faster and reach the end of the tube first.

There was also a multiple choice my that had 3 tubes, one slotted, one plastic and one metal. The answer said the plastic and slotted have the magnet fall at the same time...

I learnt is as eddy currents are produced but not as strong, which seems logical.

fucking physics.

Pretty sure eddy currents will flow, but only VERY SMALL ONES. By Faraday's law any change in flux will result in EMF. The slots just minimise huge ones, don't eliminate it.



*correct if wrong*

 

[Parvee]

Pretty sure eddy currents will flow, but only VERY SMALL ONES. By Faraday's law any change in flux will result in EMF. The slots just minimise huge ones, don't eliminate it.



*correct if wrong*

Yeah that is correct. I dunno why in that hsc question they said it gets eliminated :/

 

[nightweaver066]

Pretty sure eddy currents will flow, but only VERY SMALL ONES. By Faraday's law any change in flux will result in EMF. The slots just minimise huge ones, don't eliminate it.



*correct if wrong*

Exactly what i learnt.. Although the size of the eddy currents depends on the size of the remaining metal slots but yeah whatever lol

 

[asianese]

But yeah, bear in mind - those HSC answers are SAMPLES.

They are used for marking purposes mostly - so the markers have a feel for what the responses should include.

The difference in 'sample' and 'model' is clearly evident in language courses for short answer responses. A 5 mark (largest mark in the English responding section) may have only 3 typed lines, which definitely does not correspond to the actual length or detail actually required.

I think we should take these 'samples' with a pinch of salt.

 

[RishBonjour]

But yeah, bear in mind - those HSC answers are SAMPLES.

They are used for marking purposes mostly - so the markers have a feel for what the responses should include.

The difference in 'sample' and 'model' is clearly evident in language courses for short answer responses. A 5 mark (largest mark in the English responding section) may have only 3 typed lines, which definitely does not correspond to the actual length or detail actually required.

I think we should take these 'samples' with a pinch of salt.

Hope so. But what about that multiple choice? it was a HSC question. would have lost a mark for that.

 

[Beaconite]

But yeah, bear in mind - those HSC answers are SAMPLES.

They are used for marking purposes mostly - so the markers have a feel for what the responses should include.

The difference in 'sample' and 'model' is clearly evident in language courses for short answer responses. A 5 mark (largest mark in the English responding section) may have only 3 typed lines, which definitely does not correspond to the actual length or detail actually required.

I think we should take these 'samples' with a pinch of salt.

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