Physics Unit 4 Exam discussion

[NE2000]

for the de broglie question, i said only orbits which have a circumference which is a whole number multiple of the electron's de broglie wavelength can exist, blah blah blah blah
and then i said, in orbits where standing waves are not be formed, destructive interference will occur, and the electron will spiral towards the nucleus and that wave will cease to exist[/u]
i am sure destructive interference will occur, it says so on 2007 itute trial paper solutions, but not so sure about electrons spiralling in, shit, why did i write that. can anyome confirm whether this is garbage or if it makes sense?


for the path difference question i solved 2 simultaneous equations and got 496 nm (i think similar to what /0 did)

Not sure about the spiralling in thing. I think you might have got confused with the problem with the Bohr model and classical physics, which suggests that an electron orbit would be emitting EM radiation and hence would spiral into the nucleus...

[tommyk221]

is anyone posting up a blank exam copy?

also with the magnet (q4), was it ok to draw lines going from top to bottom (i.e. like a normal bar magnet) without going through the bar?

Try here for a blank paper:
http://vcenotes.com/forum/index.php/topic,19792.0.html

[TrueTears]

is anyone posting up a blank exam copy?

also with the magnet (q4), was it ok to draw lines going from top to bottom (i.e. like a normal bar magnet) without going through the bar?

Yeah that's what I did. An electromagnet behaves like a permanent magnet... Anyone else (TT, /0 ?)

That one where you had to draw 4 lines?

I had the lines going in from the bottom out around the top and back in the bottom.

[/0]

is anyone posting up a blank exam copy?

also with the magnet (q4), was it ok to draw lines going from top to bottom (i.e. like a normal bar magnet) without going through the bar?

Yeah that's what I did. An electromagnet behaves like a permanent magnet... Anyone else (TT, /0 ?)

Yeah it's probably ok. I guess VCE physics is like that... they don't tell you to draw inside bar magnets (and they don't tell you not to).

But really... every magnetic field is a closed loop.

[TrueTears]

is anyone posting up a blank exam copy?

also with the magnet (q4), was it ok to draw lines going from top to bottom (i.e. like a normal bar magnet) without going through the bar?

Yeah that's what I did. An electromagnet behaves like a permanent magnet... Anyone else (TT, /0 ?)

Yeah it's probably ok. I guess VCE physics is like that... they don't tell you to draw inside bar magnets (and they don't tell you not to).

But really... every magnetic field is a closed loop.

Yeah so is it ok if I drew through the "bar magnet"? Cause I remember what you said... must be a closed loop.

[homghomg1]

is anyone posting up a blank exam copy?

also with the magnet (q4), was it ok to draw lines going from top to bottom (i.e. like a normal bar magnet) without going through the bar?

Yeah that's what I did. An electromagnet behaves like a permanent magnet... Anyone else (TT, /0 ?)

yeah, it said in the region around the iron core
i don't think the iron core is necessarily a permanent magnet anyway, it just helps to channel the magnetic field by increasing its strength (cos it's a temporary magnet when subject to the field of the wires? not sure on this)
anyway, i think you just had to draw the 4 lines going from bottom to top, and show them coming back to the bottom on the outside of the wires as well if you wanted to be sure

[ayaz]

for the iron core Q i drew the lines inside the iron would i get full marks???

[homghomg1]

for the de broglie question, i said only orbits which have a circumference which is a whole number multiple of the electron's de broglie wavelength can exist, blah blah blah blah
and then i said, in orbits where standing waves are not be formed, destructive interference will occur, and the electron will spiral towards the nucleus and that wave will cease to exist[/u]
i am sure destructive interference will occur, it says so on 2007 itute trial paper solutions, but not so sure about electrons spiralling in, shit, why did i write that. can anyome confirm whether this is garbage or if it makes sense?


for the path difference question i solved 2 simultaneous equations and got 496 nm (i think similar to what /0 did)

Not sure about the spiralling in thing. I think you might have got confused with the problem with the Bohr model and classical physics, which suggests that an electron orbit would be emitting EM radiation and hence would spiral into the nucleus...

"energy levels of the atom could not be explained in terms of the Newtonian model , since orbiting objects are by definition accelerating and should therefore be gradually losing energy, and thus should be expected to spiral in towards the nucleus eventually crashing into it. But this was not in accord with the observed facts. What therefore was it that kept the electrons within their discrete ‘scale-like’ positions at particular distances from the nucleus"

this is from some website. hmm I don't know, it does say that they are expected to spiral in towards the nucleus according to the newtonian model, and the reason they don't (as De Broglie discovered) is due to the presence of standing waves. Ughh.. I hope they don't mark me down :/

[TrueTears]

for the iron core Q i drew the lines inside the iron would i get full marks???

I don't know, I remember /0 saying every magnetic field must be a closed loop so I drew them through the iron.

[NE2000]

is anyone posting up a blank exam copy?

also with the magnet (q4), was it ok to draw lines going from top to bottom (i.e. like a normal bar magnet) without going through the bar?

Yeah that's what I did. An electromagnet behaves like a permanent magnet... Anyone else (TT, /0 ?)

Yeah it's probably ok. I guess VCE physics is like that... they don't tell you to draw inside bar magnets (and they don't tell you not to).

But really... every magnetic field is a closed loop.

If it were a bar magnet you wouldn't lose any marks for not going through it. If it were a solenoid you would have to go through it. So the issue is that because it is an electromagnet, is there extra significance to the fact that the field lines travel through the core? Is there any significant difference between the actual magnetic properties of an electromagnet and a bar magnet?

[/0]

is anyone posting up a blank exam copy?

also with the magnet (q4), was it ok to draw lines going from top to bottom (i.e. like a normal bar magnet) without going through the bar?

Yeah that's what I did. An electromagnet behaves like a permanent magnet... Anyone else (TT, /0 ?)

That one where you had to draw 4 lines?

I had the lines going in from the bottom out around the top and back in the bottom.

Yeah that's kinda what I did with the outer two lines, but with the inner two I didn't loop them, I just let them go off the page

All my lines went through the bar magnet

[TrueTears]

is anyone posting up a blank exam copy?

also with the magnet (q4), was it ok to draw lines going from top to bottom (i.e. like a normal bar magnet) without going through the bar?

Yeah that's what I did. An electromagnet behaves like a permanent magnet... Anyone else (TT, /0 ?)

Yeah it's probably ok. I guess VCE physics is like that... they don't tell you to draw inside bar magnets (and they don't tell you not to).

But really... every magnetic field is a closed loop.

If it were a bar magnet you wouldn't lose any marks for not going through it. If it were a solenoid you would have to go through it. So the issue is that because it is an electromagnet, is there extra significance to the fact that the field lines travel through the core? Is there any significant difference between the actual magnetic properties of an electromagnet and a bar magnet?

I think they're exactly the same just that an electromagnet is not permanent and lose its magnetism as soon as the current is turned off. Thus it acts just like a bar magnet as long as there is current.

[homghomg1]

lol I think the iron bar occupies pretty much the whole space inside the wires, so it'd be hard to draw the lines not going through it

[NE2000]

lol I think the iron bar occupies pretty much the whole space inside the wires, so it'd be hard to draw the lines not going through it

No I think you are misinterpreting what I'm saying. I had my field lines starting at the north end and looping around going to the south pole. I didn't draw them going through the iron core.

[almostatrap]

with the iron bar, i think everyone will get fulls marks either way. you cant lose marks for adding in detail