Homework 2 solutions
are here. I'll add Quiz 2 & 3 solutions tonight or this weekend.
Friday, July 13, 2012
Thursday, July 12, 2012
Thursday's lab
is all about circuit elements and learning to wire things up. There are two files: an 'intro' one to walk you through how to use the test equipment, and a procedure for the actual lab. This one will again be a bit more inquiry-based, the main idea is really just to wire stuff up and see what happens ... and then explain why it happened.
[Yes, there will be a quiz, it will be on capacitors.]
[Yes, there will be a quiz, it will be on capacitors.]
Today's lab
was probably a bit hard for you. That is OK. There are really two reasons for this.
1. Scheduling. I chose to do relativity first, the other two classes I have to stay synchronized with lab-wise did not. My way is sort of a pain on the instructor (not following the textbook order for one), but I think the course as a whole ends up more coherent. Also, the PH106 section we're syncing with doesn't even cover relativity at all. As a result, for the first week or so the labs come a bit sooner than I would like. This will be resolved next week.
2. Realism. You walked into the lab knowing only a little bit about capacitors, and then were expected to figure out how they acted in combination - while also knowing next to nothing (on average) about the power supply and meter you were supposed to use. This probably meant you were confused at first, had to read and think a bit, and ask a lot of questions about the equipment. It is frustrating, but this is a much more realistic picture of how real experiments work - many unknowns, all you can do is be systematic and careful. It is more a barely-guided exploration, driven by your inquiring as to how things work, than baking a cake or assembling some Ikea furniture. There is never a complete recipe or instruction manual that will always work. We can't do all the labs like this - just throw you into the fire, as it were - but I think it is a good experience to just turn you loose with minimal preparation and see what you can figure out some times. We will do some 'cake baking' labs too, but doing only those gets boring.
That being said, tomorrow in lecture we'll discuss capacitors, meters, and circuits in detail, and I think in retrospect everything will make sense, and you'll have a better appreciation for what you did today.
Tomorrow's lab is a milder version of the same thing - we're going to turn you loose with various electrical components and see what you can make them do. It will be less difficult than what you did today, but will still involve an element of exploration that is really key to proper experimentation.
1. Scheduling. I chose to do relativity first, the other two classes I have to stay synchronized with lab-wise did not. My way is sort of a pain on the instructor (not following the textbook order for one), but I think the course as a whole ends up more coherent. Also, the PH106 section we're syncing with doesn't even cover relativity at all. As a result, for the first week or so the labs come a bit sooner than I would like. This will be resolved next week.
2. Realism. You walked into the lab knowing only a little bit about capacitors, and then were expected to figure out how they acted in combination - while also knowing next to nothing (on average) about the power supply and meter you were supposed to use. This probably meant you were confused at first, had to read and think a bit, and ask a lot of questions about the equipment. It is frustrating, but this is a much more realistic picture of how real experiments work - many unknowns, all you can do is be systematic and careful. It is more a barely-guided exploration, driven by your inquiring as to how things work, than baking a cake or assembling some Ikea furniture. There is never a complete recipe or instruction manual that will always work. We can't do all the labs like this - just throw you into the fire, as it were - but I think it is a good experience to just turn you loose with minimal preparation and see what you can figure out some times. We will do some 'cake baking' labs too, but doing only those gets boring.
That being said, tomorrow in lecture we'll discuss capacitors, meters, and circuits in detail, and I think in retrospect everything will make sense, and you'll have a better appreciation for what you did today.
Tomorrow's lab is a milder version of the same thing - we're going to turn you loose with various electrical components and see what you can make them do. It will be less difficult than what you did today, but will still involve an element of exploration that is really key to proper experimentation.
Wednesday, July 11, 2012
Wednesday's lab
is all about capacitors. We will start to discuss capacitors in Wednesday's lecture before the lab, and use the lab period to verify some of the things we'll discuss.
To be perfectly honest, it is a fairly simple little lab that is as much intended to get you used to operating electrical equipment as it is to prove various things about capacitors. You won't really have to apply the uncertainty analysis you learned on Monday just yet either, but that will come back soon enough. In light of this, take Wednesday as an opportunity to do a relatively simple procedure carefully and really get the hang of connecting electrical components and wiring things up. You can also take advantage of the lab time to ask the TAs questions about homework or lecture material.
In Thursday's lab we will start to learn about circuits. It will also be relatively simple in principle, but the explanations for what you will observe will be more subtle. Paying attention on Wednesday and getting used to wiring things up will pay off on Thursday.
To be perfectly honest, it is a fairly simple little lab that is as much intended to get you used to operating electrical equipment as it is to prove various things about capacitors. You won't really have to apply the uncertainty analysis you learned on Monday just yet either, but that will come back soon enough. In light of this, take Wednesday as an opportunity to do a relatively simple procedure carefully and really get the hang of connecting electrical components and wiring things up. You can also take advantage of the lab time to ask the TAs questions about homework or lecture material.
In Thursday's lab we will start to learn about circuits. It will also be relatively simple in principle, but the explanations for what you will observe will be more subtle. Paying attention on Wednesday and getting used to wiring things up will pay off on Thursday.
Solutions and such
I have solutions for quiz 1 and homework 1. You'll get your graded HW1 back tomorrow (Wed), I suspect the TAs will have the quizzes back to you shortly as well.
Tuesday, July 10, 2012
Tutoring
We have one undergrad physics major who is game for doing some tutoring over the summer if anyone is interested. Send me an email, and I'll forward his contact information. Don't want to put his email & phone numbers online for obvious reasons ... he did some tutoring for a few PH105 students during the last summer semester, and it seemed to work out well for them.
Monday, July 9, 2012
HW hints
For the first problem:
For the third problem, the proton sees a contracted length. It would observe a time consistent with this distance divided by the relative velocity, whereas in the laboratory we would observe a time which is the rest length of the tube divided by velocity.
For the last problem, the difference between dilated and proper time is 2s every 86400s. This must mean that the spaceship clock runs a factor (1+2/86400) slow.
- http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/polebarn.html
- http://en.wikipedia.org/wiki/Ladder_paradox
- http://www.xs4all.nl/~johanw/PhysFAQ/Relativity/SR/barn_pole.html
For the third problem, the proton sees a contracted length. It would observe a time consistent with this distance divided by the relative velocity, whereas in the laboratory we would observe a time which is the rest length of the tube divided by velocity.
For the last problem, the difference between dilated and proper time is 2s every 86400s. This must mean that the spaceship clock runs a factor (1+2/86400) slow.
Tomorrow's lab
will be on uncertainty analysis, a short experiment in counting cards. There will be a quiz during the lab period on relativity - very similar to problems I went over in lecture. It will be mostly about time dilation and length contraction.
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