TrueTears question thread

[TrueTears]

Did you get the correct answer? I would've said that the initially the magnetic field was increasing DOWNWARDS, as the magnetic field is drawn for N into S. The initial induced current must thus produce an upwards flux, and is therefore anticlockwise.

But you never know. I could be wrong... I'm doing other homework at the moment, so maybe I misread the diagram or did something careless

Yeah, it is the right answer, I tried vector method as well and got the same thing.

I think it's a bit tricky because it has the south pole on the bottom which means the magnetic field is coming IN to the south and going through the magnetic to north, ie, the magnetic field is going up rather than down. If you had north pole on the bottom,then it'd be going downwards as its coming OUT of the north and into the south.

[appianway]

Ahh that would explain it. Maybe I should have spent more time looking at it... >.< In that case, your explanation's perfect

[TrueTears]

Ahh that would explain it. Maybe I should have spent more time looking at it... >.< In that case, your explanation's perfect

Awesome, thanks appianway!

[TrueTears]

Also why doesn't LED emit light with discrete wavelength?

Like I know why a sodium lamp emits light of discrete wavelength because each electron jumps a shell and emits a photon which corresponds to the change in energy between the 2 energy levels, what happens in a LED?

Thanks

[appianway]

Well, according to the reliable source of Wikipedia, the photons emitted correspond to the band gap energy between the P and N junctions. As I'm sure you already know from unit 3, the electrons in LEDs "fill" holes and hence drop energy levels. I'm not sure precisely why the LED doesn't emit light with a discrete wavelength though (it sounds like it should be!), but presumably the wavelength's within a certain range.

[TrueTears]

Well, according to the reliable source of Wikipedia, the photons emitted correspond to the band gap energy between the P and N junctions. As I'm sure you already know from unit 3, the electrons in LEDs "fill" holes and hence drop energy levels. I'm not sure precisely why the LED doesn't emit light with a discrete wavelength though (it sounds like it should be!), but presumably the wavelength's within a certain range.

Hmm yeah I thought the same, I thought they'd emit a range of wavelength but each photon emitted should have a "discrete" wavelength? Not sure heh.

[TrueTears]

ty

[/0]

If we assume we're generating a fundamental standing wave,



, with gradient

Using a line of best fit on the data (i cheat with regression):







Ok, nevermind... maybe this was meant to be a second harmonic........ is this from insight :/

[TrueTears]

If we assume we're generating a fundamental standing wave,



, with gradient

Using a line of best fit on the data (i cheat with regression):







Ok, nevermind... maybe this was meant to be a second harmonic........ is this from insight :/

I did exactly what you did /0... funny thing is it says "loudest" which meant I thought it was fundamental, but 671.2 lol too fast for speed of sound =.=

[TrueTears]

1.


I thought answer was C but according to the solutions it's B, are they wrong?

2.


I said A was blue and B was red, but answer is vice versa, are they wrong?

3. I have also noticed that when a question asks "find the minimum energy of a photon that will cause an electron to escape" and a graph of E_k - freq is provided. There are 2 ways of doing it, one is to read off the y intercept, the Work function, but the other way is to do f_0h and find f_0 from the x axis. However in 2 exams, they've all done the x f_0h method and the Work function method tends to give slightly different answers ~0.4-0.5 off (in eV). So what method do you do? Would both be considered right?

Many thanks guys!

[/0]

I get the same answers are you :p

[kurrymuncher]

1. minimum photon energy for silver surface is half, so its work function has to be half of sodium. I get C too. ?

2. Red light has a larger wavelength than blue, so it should have larger fringe spacing, So I would also say B is red and A is blue. hmmm. which exam is this from?

[TrueTears]

2008 Lisachem, very very bad... too many mistakes, I can not remember one trial exam I've done that hasn't had a single mistake ffs.

Anyways, thanks heaps for your help guys!

[TrueTears]

What's the question even asking? I have no idea what it even means. The answer is C btw.

[kurrymuncher]

LOL that is a shit question. Its almost like they are asking you to state the range and domain of that graph. lemme guess....Lisachem??