Several Things I would recommend for studying for the final:
First, go through all posts of the last month on this site, especially things like "Notes on..." or "...what we should know". Try to understand those posts and ask questions, as comments on this web site, regarding anything you do not understand. The more specific the questions are, the better, but just ask about anything that you are confused about. This is very important.
If you ask via a post here, please be clear about what topic and post you are referring too. I will also try to check for questions at the end of all recent posts.
Second, try to understand the last 2 quizzes and most problems from all HW since the midterm, as well as any HW on the relationship of temperature to microscopic motion and on energy and especially potential energy from the first half of the class. Ask questions about that also via comments to this post.
Topics that will be emphasized for the final are:
1) quantum physics: implications of the uncertainty principle; quantum jumps that involve light emission or absorption; and maybe something related to spectroscopy or color.
2) the nature of conducting materials; the difference between a metal and a semiconductor or insulator from an atom/electron counting point-of-view. Bonus if you understand the relevance of the uncertainty principle here.
3) Simple circuits: the relationships between I, V, and R; and also energy disipation and power in circuits P=V I (Watts). Understand that I = amperes = coulombs/second; and P= Watts = Joules/second. Know what that means.
4) the motion of a mass in a potential energy, like the problem (5) on the midterm. If you are truly comfortable with that, it will be valuable.
5) possibly something related to temperature and how, in absolute units, it is fundamentally related to atom motion (in a gas).
Finally, keep checking this site for updated information and, especially, discussion stimulated by student questions.
I'll add practice problems here as I come up with them. These are only a supplement to the above guide and topic outline. (As discussed in class, it is ok to bring a 3x5" card of equations, relationships and units to the final. Please don't get carried away.)
For a circuit with a battery, wire and resistor, describe the what happens in the circuit including the current flow and especially the energy conversion processes.
For a circuit with a battery, wire and a light bulb, describe the what happens in the circuit including the current flow and especially the energy conversion processes.
For a circuit with a 10 Volt battery, wire and 5 Ohm resistor, how much current flows though the resistor? How much heat energy, in Joules, appears in the resistor each second. How much in 5 seconds?
For a circuit with a 10 Volt battery, a resistor and wire (all in series), suppose there is 3 coulombs per second flowing through the wire. How much current flows though the resistor? How much heat energy, in Joules, appears in the resistor each second. How much in 4 seconds?
extreme extra credit: Describe the energy conversion processes associated with an LED (light emitting diode). Is there a quantum jump involved??
For blue light, what is the wavelength, frequency and energy of a typical photon?
For red light, what is the wavelength, frequency and energy of a typical photon?
Discuss the relationship of temperature to microscopic atom motion in a noble gas.
For a composite gas, like air, in thermal equilibrium, do heavier atoms tend to move more slowly than lighter atoms? Explain why. What are your basic assumptions?
Explain the uncertainty principle and its relevance to understanding the origin of the size of atoms.
What is the wavelength, frequency and energy of a green photon?
Present an illustrated discussion of atomic spectra, including what they are, why they were unexpected, and what people infer from atomic spectra regarding the nature of the energy levels of an atom.
Suppose an electron in an atom has allowed quantum energy levels at exactly 2 eV, 4 eV, 5 eV and 5.5 eV. If 2 eV is the energy of the ground state and all the atoms in a cold gas start out in the ground state, what are the a) energies, b) frequencies and c) wavelengths of possible quantum absorption events in which a single photon is absorbed and the electron jumps from the ground state to another state? (actually, you can start with d) if you like and then do parts a), b) and c)...)
d) How many sharp lines would there be in the absortion spectrum for this atom?
e) Make a graph of an absortion spectrum for this atom.
f) Are these absorptions in the infrared, visible or UV? If visible, what color are they?
For green and orange light, what are the wavelengths, frequencies and energies of typical photons, respectively?
What is the composition of He? What is the composition of an He+ ion? What is the difference between He+ and He? What is the difference between He+ and H?
Subscribe to:
Post Comments (Atom)
where/when is the final?
ReplyDeletenever mind. got it
ReplyDeleteWhere/when is it?
ReplyDeletePlease post answer.
Also it is so hard to create an account to post stuff, it keeps telling me ive made errors. I tried signing up earlier in quarter but gave up.
But i really want to know when final is
Thursday, March 19th, 4:00-7:00pm, same room as the lecture.
ReplyDeleteDo we need to memorize all the atom compositions and specific color wavelengths?
ReplyDeleteWhat if you put the elements, from H to Ne, on one side of your 3 x 5 card? Just the number of protons, neutrons and electrons for those atoms. There should be room, since there is not much else you would need. Maybe then add things like f=c/lamda, E=hf, values of h. What else? Maybe circuit related equations. Does anyone have any other suggestions/questions?
ReplyDeleteRegarding colors, I just found this web site:
ReplyDeletehttp://eosweb.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html
Maybe just put a few "benchmarks" on your card:
650 nm is red (633 nm is the wavelength of a Helium- Neon Laser and that is also red)
500 nm is green, slightly bluish-green
400 nm is violet
(and c = 3 x 10^8 m/sec)
Note that the wavelengths are often in nm (10^-9) and you need to take that into account in calculating frequency from wavelength (cause c is usually in meters (per second).
I'll post some answers later that you can check you solutions against. As you probably realize, I believe, that it is important to do you own solutions before you check the answers.
ReplyDeleteI would rather you put the atoms from He to N on the test, but if not I'll suck it up and put it on my 3x5 card.
ReplyDeleteAlso, when I was looking back at some of the posts (i.e. the Virtual Quiz posts) there are extra credit questions, should we know these for the final?
Which ones do you mean? What were they about?
ReplyDeleteIf you mean the one about superconductivity, then no.
From March 4th's post called HW on Conducting Materials and Circuits: Solutions and Discussions
ReplyDelete3. (extra credit) What are unusual macroscopic and microscopic characteristics associated electrical conduction of a superconductor?
On a macroscopic level, superconductors are unusual in that they conduct electricity with ZERO resistance. Other metals have resistance. Superconductors have no resistance at all. They are “frictionless” even if there is some disorder in their structure. This was very surprising. It took more than 50 years for scientists to solve the mystery of superconductors. Part of the solution leads to the surprising result that electrons in superconductors pair with each other! On a microscopic level the electrons in a superconductor are paired. For reasons that are difficult to explain and related to a quantum property known as “phase” pairs of electrons move with zero resistance.
4) Based on considerations similar to those you used in the above problems (from the quiz), discuss your thoughts on what the nature of gold (Au) might be. Include discussion of the total number of electrons per atom, how many might stay localized and how many, if any, go into non-localized states...
4. Gold is difficult since it has so many electrons to wonder about. Wow, it has 79 electrons and the nearest noble gas is Xe, which has 54 electrons. The bottom line is this : 1 electron per Au atom goes into the electron sea. Those are the ones that are responsible for the conductivity. Of the ones left behind, 10 are in a filled d-level “mini-shell”, 14 are in a filled f-level “mini-shell”. I am amazed that the counting then seems to work: 54 + 14 + 10 +1 = 79. The last 1 is the one that counts for conductivity. Sorry. Didn’t realize this would be quite so hard. My mistake. I thought it would be interesting because gold is a familiar material and a good conductor. Copper, silver and gold are all in the same column of the periodic table and all similar metals.
5) (Extra credit) Do the same for Ge (germanium). [Hint: For Ge, try assuming that there is a core which is like Ar (argon) but with exactly 10 extra electrons filling a "d-state mini-shell"
5. Ge is like Si except the noble gas core is the next one down and there is a filled d-level mini-shell in addition to the 4 electrons in covalent bonds (as in Si). So it is a semiconductor with a phenotype very similar to Si.
6) [Extra credit) If Ge is similar to Si, then speculate as to what a semiconductor which is exactly half Ga atoms and half As atoms (gallium and arsenic) would be like. Assume that they are in a perfectly ordered structure with each Ga having 4 nearest neighbors of As and visa versa. (Ask me to draw this in class if you like). How many electrons does each atom have, where do they go, etc? Is this similar to salt* or to Si or ...?
*NaCl
6. This is very hard problem, but important since GaAs is a very common and useful semiconductor (lasers, LED’s…). Ga and As are on either side of Ge, so if each As gives each Ga one electron then they can formed a semiconductor with 4 covalent bonds to nearby neighbors just like Si and Ge. In the since that each Ga receives one electron from each As, it is sort of like a NaCl, where each Na loooses an electron to each Cl forming a lattice of Na+ and Cl-. Through this ionic electron exchange, however, it becomes a semiconductor, like Ge and Si. This raises the interesting question "Why isn't NaCl a semiconductor?" which we won't answer here.
From same post but from the book Ch. 23 problem 6 (p.457 in textbook)
6) P=I V . In this case 4 Watts = I x 120 Volts, so I =4/120 = (1/30) amps
b) R=V/I = 120 V/(1/30 amps)=30x120 Ohms = 3600 Ohms.
c) 4 Watts = 4 Joules/sec. There are about 365 x 24 x 60 x 60 seconds in a year. So the total power utilized in one year is 4 x (365 x 24 x 60 x 60) (Joules).
d) to get watt hours in one year we multiply 4 watts times the number of hour in a year, which is 365 x 24. Then divide by 1000 to convert from watt-hours to kilowatt-hours.
Total cost would then be: $0.15 x [4 x (365 x 24)].
These are the extra credit questions i was wondering whether were on the final or not.
Also, could you post the solutions to HW for Ch 26, 27, and 30 (from post called Homework on Light; newest version with some problems deleted, on March 3)
-Eleanor
What exactly should we know about temperature? Can you explain a little bit about Kelvin? And how is it "fundamentally related to atom motion (in gas)"? I'm a little lost.
ReplyDeleteEleanor, for those above, I would say you do not need to review any of them except the first parts of 6, (a, b and c), and for c) think about it in terms of a short time like 5 seconds or 10 seconds (4 J/s x 5 s = 16 Joules)...
ReplyDeleteOtherwise, I don't think there would be anything on these more complex materials, though you should be prepared to answer questions about or discuss materials like Cu, Al and Si, and perhaps P-doped Si. Does that seem reasonable? Please let me know if the reply needs details or elucidation.
Kayla,
ReplyDeleteWell, the fundamental starting point is that we assume/believe that the temperature of a gas is proportional to the kinetic energy of an average molecule (or average kinetic energy of the molecules). Really thinking about what that means is the key. For example, it means that if you add up the kinetic energy of all the atoms in the gas, and divide by the number of atoms, that will give you a number proportional to the temperature. So, for example, in thermal equilibrium a helium gas with 1000 atoms would have half as much total energy as a helium gas with 2000 atoms, but they would have the same temperature. (Since the 2000 atom gas has twice as many atoms running around with the same average kinetic energy.) So temperature can be viewed as a quantity that does not depend on the system size, but only on what the average atom is doing.
And, this is important, but has been understated, the proportionality "constant" is the same for all gases; so how would the total energy of a gas of 500 He atoms compare with the total energy of a gas of Ne atoms, which are heavier?
Eleanor,
ReplyDeleteGood point. I added the solutions for the problems on light, etc, to the March 3 post, Homework on light: newest version with solutions.
In the equation E=hf, what is h?
ReplyDeleteAlso, you said in lecture that you would be posting the periodic table, is this still correct? And when are you posting the answers to the problems above?
ReplyDeleteAndrew, I am not sure what you mean by that? That could be a very deep question? Have you read the earlier posts which relate to h? would some students please respond/comment on "what is h?"
ReplyDeleteKayla,
Later today or tonight I will post some answers. Actually if you would post some of yours I will respond ASAP. That is actually much better in the sense that you will learn more.
for the first quantitative problem.. given a battery of 10 volts and a 5 ohm resistor, I got that the current will be two coulombs per second and that the power that passes into the resistor will be 20 joules per second.. over 5 seconds this would be 100 joules passing through. am I on the right track?
ReplyDeletealso how do we measure the heat energy in a resistor?
ReplyDeletefor the second one, the question is slightly redundant. We are given that I=3 Coulombs/second and V=10.. it doesn't ask for R but I believe that would be 10/3. if you use the P=VI equation, P=(10)(3)= 30 Joules/second passing through the resistor every second.. in 4 second 120 joules will have passed through. Am I wrong?
ReplyDeletewhat should we use for Planck's constant?
ReplyDeleteWill. Nice. Everything you say looks very right to me and very well explained. For Planck's constant let's use both eV-sec and Joule-sec (put them on your card). There may not be a question that uses it, but I am still working on that and I think you should have them on your card. I think it is 4.14 x 10^ -15 in ev-sec. (The minus sign is very important!) So that means, i suppose, that a photon of 10^15 sec-1 would have an energy of 4.14 eV, right?
ReplyDeleteNot exactly sure what you mean about measuring the heat of (generated in) a resistor. I mean, you could stick it in a known amount of water or something and see how much the temperature changes?
i thought we are not getting any problems that deal with big exponents
ReplyDeletealso I remember you saying that we only need to know Copper and Aluminum when it comes to memorizing electrons, protons, and neutrons of an element. So do we really need to memorize H through Ne? With all due respect, I feel like you are constantly changing your mind with certain topics. I'm just getting confused on what to put aside and what to focus on. Lastly, for this problem:
ReplyDeleteFor a circuit with a 10 Volt battery, a resistor and wire (all in series), suppose there is 3 coulombs per second flowing through the wire. How much current flows though the resistor? How much heat energy, in Joules, appears in the resistor each second. How much in 4 seconds?
I dont get the last part of the question, involving heat energy
Thank you
I see your point and would like to say that your focus is very good. Perhaps you are overinterpreting comments here? You do not have to memorize or focus on any elements other than Cu and Al. My response regarding writing 10 elements on a card, which would take a few minutes, does not make it a point of focus. You do not need to memorize or focus on them (H through Ne).
ReplyDeleteThe points of focus have not changed and earlier posts regarding that are worth looking at. I would also add that there is only one circuit problem on the final. They are getting a lot of play in the discussion here, but that doesn't mean people should see them as a larger focus area than previously stated.
I am still trying to write a final without any big exponents, but that doesn't mean that I would discourage people from putting h on a card in a class that has a big modern physics (quantum) emphasis.
Finally the problem you mention was solved by Will above so I am not sure what you are asking. Can you maybe explain? In a resistor electron potential energy gate turned into heat. The amount is as above.
for the last problem...
ReplyDeleteWhat is the composition of He? What is the composition of an He+ ion? What is the difference between He+ and He? What is the difference between He+ and H?
What notes should I look at to figure this problem out. This does not have to do with deterium does it?
No. What is the composition of He?
ReplyDelete(Let's start with that)
ReplyDeletehelium is 4 amu, and has two electrons
ReplyDeleteYes, 2 electrons. perfect. So what is He+ ?
ReplyDeletethats where i get confused, when an ion comes in. is it 3 electrons?
ReplyDeleteYou said in lecture that you would put up a periodic table for us to use during the final, is this still true?
ReplyDeletefor this question:
ReplyDeleteSuppose an electron in an atom has allowed quantum energy levels at exactly 2 eV, 4 eV, 5 eV and 5.5 eV. If 2 eV is the energy of the ground state and all the atoms in a cold gas start out in the ground state, what are the a) energies, b) frequencies and c) wavelengths of possible quantum absorption events in which a single photon is absorbed and the electron jumps from the ground state to another state? (actually, you can start with d) if you like and then do parts a), b) and c)...)
d) How many sharp lines would there be in the absortion spectrum for this atom?
e) Make a graph of an absortion spectrum for this atom.
f) Are these absorptions in the infrared, visible or UV? If visible, what color are they?
can you do like a step by step process of how to approach this problem? for a, do you just add up all the numbers since eV stands for energy(I think) I know Ev is equal to hf, but how do you find f? I know we are given h. I guess we can solve for c(wavelength) once we are given frequancy, since we know what c is. Will we get 5 sharp lines in the spectrum? I don't know how to do F at all. Am I kinda in the right track?
bball: He+ has just one electron (not 3) one electron and two protons. (hence +) Does that make sense?
ReplyDeleteFor the next one you asked, the energies of possible absorbed photons are the differences but starting out in the ground state. Start by figuring out just that --the photon energies-- and indicate what transition each one is associated with.
Kayla, Yes, I will bring a periodic table to put it. It will not be a major point of focus at all.
Regarding the content of the final, about half of the final is essay type questions. There are two problems that involve calculation and problem solving, and a few short answer questions. One of the longer problems involves a potential energy as a function of x.
ReplyDeleteThe short answer questions are very straightforward, one involves h and another involves c, so please be sure to put h and c on your card. They are a small part of the final but you may as well be prepared for them.
Regarding big exponents, what i did was try to keep them out of long, involved problems, like on the HW, where messing them up leads to further problems down the road. They are fully isolated in short answer questions that don't effect anything else. I think that's reasonable.
a potential energy as a function of x, is the same idea as problem 5 on the midtern, where potential energy equaled 1/2mv^2
ReplyDeleteA couple more hints and answers:
ReplyDeleteFor the: "Suppose an electron in an atom has allowed quantum energy levels at exactly 2 eV, 4 eV, 5 eV and 5.5 eV. If 2 eV is the energy of the ground state and all the atoms in a cold gas start out in the ground state...." problem, I think there would be sharp absorption lines at 2 eV, 3 eV and 3.5 eV (why?). You can use h= 4.14 x 10^ -15 eV-sec to get the frequency in sec-1 ....
-----
For a green photon suppose that lamda = 500 nm. then f = 6 x 10^14 sec-1 (or cycles per second or Hz).
For bball's last question (regarding an electron at allowed quantum energy levels) I'm thinking to maybe use the conservation of energy: hf+E1=E2 to find the energies? Am I at least on the right track? Also, would the absorption spectrum have 5 sharp lines like bball said, because I was thinking it was three? But I'm not sure...
ReplyDeleteAnother quick question, is there a limit to how much we can put on our 3x5 card?
Thanks!
Just to be sure,
ReplyDeletered is 650 nm
green is 500 nm
what is blue?
you said violet was 400 nm.
And will we need to know problems like this?
ReplyDelete#3 of a quiz:
An ideal gas initially has a temperature of 27 degrees C and the average speed of He atoms in the gas is 500 m/s. Heat is added to the gas until the average speed of the He atoms is measured to be 1000 m/s. What is the temperature after the heat is added?
Oh! I think I got it. I forgot to refresh the page and didn't see your other two responses. That helps a lot. Thank you!
ReplyDeleteKayla, You know enough about color. Forget about the little factiods and think about the big picture questions and issues.
ReplyDeleteAnnahs,
You are correct that there are just 3 absorption lines and yes it is based on cons of energy, just like you said.
Kayla, If the speed is doubled, the temperature would be a factor of 4 higher cause it is proportional to v^2. I won't ask you that on the final.
What is our starting point for relating temperature to micro motion?
temperature (degrees K) is proportional to KE
ReplyDeleteSorry one last thing, can you please post the answers to the problems you asked?
ReplyDeleteThe problems for which it would be helpful or appropriate to post answers have already been answered above (in this comment string).
ReplyDeleteThe practice problems posted above are good training problems to work on a few days before the final or yesterday, but some of them are computationally more challenging than the problems on the final, and, at this point, I think it is preferable to change your focus to thinking about the larger issues and deeper meanings. Do you understand the concept basis behind these sort of problems?
The final will have some computation, but mostly it will have a conceptual focus.
Hi, could we talk about f=c/lamda and E=hf?
ReplyDeleteAll I have in my notes regarding c is that it equals 3*10^8, but what does that signify?
For the h, I believe it is Planck's constant (4.14*10^-15?) but in one lecture I thought we talked about it as being pretty negligible in terms of energy levels.
Thanks!
ah, c is speed of light? i think i've got it then
ReplyDeletelodi dodi
ReplyDeleteas the class is wrapping up, I just want to clarify that we will get credit for the online homework you required in the first part of the class? we paid for that and would like to receive the points we earned. thank you.
ReplyDeleteAfter reading everything, do we need to know the numbers for the wavelengths of specific colors?
ReplyDeleteall the constants like c and h MUST have units.
ReplyDelete3 x 10^8 by itself means nothing!
3 x 10^8 m/s is the speed of light (c).
h is planck's constant. It can be in either ev-sec or Joule-sec (your choice). The numerical values are different (by about 1.6 x 10^-19.)
I think you should be familiar with h and have it on your card.
There is no need to know anything about colors for this test.
i totally agree with weirdor. We did not only pay for this online homework thing, we also invested a GOOD amount of time into it. It is only fair that we get homework credit for it. It simply would not be right otherwise. thank you zach.
ReplyDeleteThis comment has been removed by the author.
ReplyDeleteThat was harder than I thought.
ReplyDeleteBut, thanks for a great quarter!