Homework Help Thread

Discuss literature (e.g. books, newspapers), educational studies (getting help or opinions on homework or an essay), and philosophy.

Unread postby Lion's Mane » Sun Jul 13, 2003 4:30 am

Jess, one quick question I have to ask. What kind of calculator are you using now? Since as far as I can see, you've got everything right. I'm guessing it's an HP though, am I correct?
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Unread postby Shi Jing Xu » Sun Jul 13, 2003 5:07 am

It's a TI-30X IIS
If I have done everything right, how do I find the initial principle quantum number if it went to n=4?
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Unread postby Seven at One Stroke » Sun Jul 13, 2003 5:53 am

Shi Jing Xu wrote:38.) An excited hydrogen atom emits light with a frequency of 1.141 X 10ˉ14 (14th power) Hz to reach the energy level for which n=4. In what principal quantum level did the electron begin?

Now, this is what I did. I figured that it was necessary to find the wavelength first, using the equation λν=c or λ= c/ν.

So my work was (c being the speed of light and ν being the frequency)
λ= 2.9979 x 10ˉ8 (8th power) meters per second/
1.141 X 10ˉ14 (14th power)sˉ
λ= 2.63 x 10ˉ22 (22nd power) meters [with all the other units canceling]


Well, first I'd like to begin by saying that I HATE quantum mechanics, because absolutely nothing makes sense to me.

Okay, secondly, it's best to do things in the simplest way possible.
You know that (delta E)=hv, and v is the frequency, so don't try to find the wavelength. (that's where you went wrong, lamda is supposed to be to the negative sixth power.

after you find out delta E, then use the equation delta E= Efin-Ein=RH(1/ni^2-1/nf^2) and plug in nf=4.

I got ni=3.2, although I'm not sure if that's the right answer or not. I just follow the steps and have no idea what I'm doing. Perhaps ni should be 4, then the answer I got is 5.99, close to 6. :roll: My guess is that the initial state is at 6, since the problem says the atom "emits" light, meaning that it's lost energy; but at the same time the problem says "reach n=4" not "drop to n=4", so it might be 3.
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Unread postby Shi Jing Xu » Mon Jul 14, 2003 2:50 am

A bit more help ^_^


54.) What is the maximum number of electrons in an atom that can have these quantum numbers?
n= principal quantum number
l= angular momentum
ml= magnetic quantum number
ms=electron spin number

1) n= 0 l=0 ml=0
2) n=2 l=1 ml=-1 ms= -1/2
3) n=3
4) n=2 l=2
5) n=1 l=0 ml= 0
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Unread postby Seven at One Stroke » Mon Jul 14, 2003 4:18 am

Shi Jing Xu wrote:54.) What is the maximum number of electrons in an atom that can have these quantum numbers?
n= principal quantum number
l= angular momentum
ml= magnetic quantum number
ms=electron spin number

1) n= 0 l=0 ml=0
2) n=2 l=1 ml=-1 ms= -1/2
3) n=3
4) n=2 l=2
5) n=1 l=0 ml= 0


Seems we're not using the same book, a pity. You might have read the book wrong (or I'm just thickheaded) but the problems actually askhing how many electrons in the atom can the same n, l, ml, ms and so on. It gave my head a spin the first time I (mis-)read it.

1) none, n>0

2)1, there's only one e- in a specific orbital with a particular spin

3) n=3 has 3s (2) + 3p (6) + 3d(10)=18 electrons total. Since nothing else is indicated, there are 18 electrons that can have n=3.

4)l<n, so none with n=2 and l=2 could exist

5)n=1, l=0, ml=0 puts the e- in the 1s orbital, with 2 possible e-. So the answer is 2.

I hope this was clear. :?
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Unread postby Shi Jing Xu » Tue Jul 15, 2003 12:18 am

Haha, now I know why good math skills were involved! Ha! Well, I tried to work it out the way you said, with the delta=hv
I got 7.56 X 10^-20 J
Then using delta E= Efin-Ein=RH(1/ni^2-1/nf^2) and plug in nf=4, I am not getting what you have. For some odd reason, I am getting -7.66 X 10^-20...........what the hell??? I suck. :cry:
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Unread postby Seven at One Stroke » Tue Jul 15, 2003 12:43 am

Shi Jing Xu wrote:I got 7.56 X 10^-20 J
Then using delta E= Efin-Ein=RH(1/ni^2-1/nf^2) and plug in nf=4, I am not getting what you have. For some odd reason, I am getting -7.66 X 10^-20


ΔE=Ef-Ei=Rh( 1/ni^2-1/nf^2)

Now that I think about it, ΔE should be negative because the atom emits light and loses energy, so:

assume nf=4
-7.5603e-20J=2.179e-18J (1/ni^2-1/16)

Divide both sides:

-0.0346960349=1/ni^2-1/16

Move 1/16 to other side:

0.0278039651=1/ni^2

Cross multiply:

ni^2=35.96609317

Take squareroot:

ni=5.997173765~=6
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Unread postby Jiang Xun » Wed Oct 08, 2003 7:27 pm

I have to do an essay on the story "War" by Luigi Pirandello, its a pain in the butt to find any info on this story, since he is most famous for his plays, so if anybody happens to find/know something, please by all means, share the wealth... :wink:
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Unread postby Seven at One Stroke » Thu Oct 09, 2003 4:23 am

What's the essay about? I think the best way to start out any (analytical) essay is to outline the points you think that are worth mentioning about the work, not the author. And in the case of this short story (which I just read over the net, so I'm not sure if it's the right one), there's really no need for any background on the author. Everything that needs to be said is in the story (which I think is a very interesting one).

First of all, why were the first two passengers arguing about who had suffered more? And secondly, why did the fat man speak so enthusiastically and seems so distanced from his own son's death? And thirdly, (which I think is where the author really shines as he rises above typical propaganda) why did he start sobbing when he realized that his own son's dead?

Well, to answer some of my own questions, I think there's one quote from King Lear that can be used: "it is not the worst, as long as we can say, 'this is the worst.'" The passengers are trying to convince each other that the other person has the worst part of the deal (either losing one of two or losing their only son), so that they know that their suffering is the worst... Why? Because if that's the worst, then nothing worse can happen to them, so they find comfort in it.

It's hard not to mix in my own opinion on the issue here, but "Country" (often capitalized in the story) is an abstract concept. What is a country? What is dying for your country? In comparison, the death of a son is solid, you cannot avoid it. You cannot dodge it with some fancy words to glorify it and forget it. Death is death. It's not a dream.

That's why I like this line a lot:

Then suddenly, just as if she had heard nothing of what had been said and almost as if waking up from a dream, she turned to the old man, asking him:

"Then...is your son really dead?"
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Unread postby Jiang Xun » Thu Oct 09, 2003 2:16 pm

Hmmmm.....i never really thought 'bout it that way....i was thinking more in the context of the lack of distinguishing details...the fact that they have no names, the fact that their story can be transplanted to any time during a confilct.
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