Scott's Ph 1 Section, Caltech 1999/2000

Physics shouldn't make you feel like this guy.

The instructor for Section 4 (prac track) is me, Scott Hughes. My office is 128 Bridge Annex, extension 8413.

I have office hours twice a week: Tuesday from 3 - 5, and Wednesday from 3 - 5. In theory, the Tuesday hours are intended to focus on the labs, and the Wednesday hours to focus on the homeworks. However, I'm not too rigid about this.

Please note that I will often move into 124 Bridge during these hours - it's bigger and has better seats. Also, if you come by 128 Bridge and find the door closed and locked, just knock (knock HARD). Alessandra and I are probably just hiding (and might have headphones on as well).

During Ph1c, I plan to move my Tuesday office hours into SAC 34. I will announce whether this plan will work or not when I find out myself (apparently I need to coordinate with the Career Development Center so I don't conflict with any interviews).

The course's main webpage can be found here (for Ph1b) and here (for Ph1c). Section 4 meets at 3 PM on Mondays and Thursday, and 11 AM on Wednesdays, in 107 Downs.

Notes on homework solutions

Your homeworks will be graded by a grad student. You want this person to be your friend: don't do things to piss him or her off! In particular, your homework should

  • Be readable. If it is so illegible that the grader can't read it, the grader doesn't have to read it. You get 0 points.

  • Be stapled if more than one page. At least one person each year seems to think that folding together the corners of multiple pages is equivalent to stapling. If you are that person, you are wrong. Keep in mind that the homework is going to get stuck inside a big envelope, shipped to the grader, put back in the envelope, shipped to me, analyzed, put back in the envelope, shipped back to you. Unless multiple pages are tightly bound, something will get lost. If that happens, oh well. Should've used a stapler.

  • Show all work. We are interested in seeing that you are learning the material. If you show all work, we can tell whether that is happening. For example, if you do a long calculation correctly, and in the final step put in g = 32 m/s2, you'll get the wrong number in the end. However, if you showed all work, we'll be able to see the process was correct and you'll probably only lose one point. On the other hand, if you didn't show any work, you could get no credit since we have no clue what you did.

  • Include units in each step. This is just plain good sense. If you are doing a calculation where you know the answer is something with units of energy, and you get the number "10" you have no idea what that means. On the other hand, if you get "10 kg m/s" you know you made a mistake somewhere, and can try to figure out where you lost the term that should've made the units kg m2/s2.

    Notes on lab writeups

    Unlike Ph1a, Ph1bc practical includes a circuit lab component. I am going to read and grade all of your lab notebooks. As I get experience with this, my suggestions to you will become more focused; for now, the following general observations:

    The lab notebook is a record of both your progress and your results as you try to do the experiment. The notes on your experiment should read almost like a diary - I want to know everything that was going on to try to understand how your lab turned out the way it did. So:

  • Include lots of information about how you do things. Sometimes the extra information contains a surprise which helps you figure out how things worked. (Don't give too much information though - I probably don't care if you changed the CD in your stereo at some point.) Sometimes you may be confused about something and the details you provide about what is going on will help those of us who are older and wiser (or just older in my case) see what might have happened.

  • Show the data exactly as you measure it, NOT as you expect it. There's always a temptation to fudge the data a bit if it doesn't look quite as you expect it to be. This is dumb. Nobel prizes have been won because the data turned out not to look as people expected. Although I doubt any of us will win a Nobel prize doing these labs, you may learn something interesting from a measurement that doesn't do what you expect.

  • Follow the homework guidelines when writing in your notebook. You can't always do this perfectly - the point of a notebook is that it follows what's going on in your head while you do an experiment. If the inside of your head is anything like the inside of mine, things aren't exactly arranged in the most pristine order. Nonetheless, try to set it up so that I can understand what you've done. At the very least, set it up so that you can understand what you've done. (It is not uncommon for people to look back at their labs after a few weeks and think ``What kind of drugs was I on when I wrote this???''. Such thoughts are a clue that you might want to try being a little more organized in your lab presentation.)

    Comments on specific experiments

    Experiment 1: I found this experiment to be fairly straightforward. One thing to notice is that some of the resistor colors are hard to read. (If you are colorblind, they may be extremely hard to read.) Take a guess at what the resistance of each resistor is supposed to be based on the color, then measure with the ohmmeter. If you are wrong, try to figure out what color you misread. (Example: I thought there were three orange-blue-violet resistors; that leads to 360 megaohms resistance. The value I measured is 360 ohms - the last color is brown, not violet.)

    Helpful tip: when soldering leads onto the batteries, you might find that the lead sticks better if you roughen the end of the battery a bit with a piece of sandpaper or a small file or something like that.

    Experiment 2: Make sure you read this all the way through before starting. Also, make sure you've got access to a second multimeter. (Since I had to do all the experiments during winter break, I had to buy one for myself.) If you are an antisocial cretin and do not know how to share, steal one: it really isn't possible to do these measurements very well without a second meter. Other than that, this experiment should be straightforward.

    Experiment 3: On the circuit diagrams, the diodes are drawn as a little arrow. Current flows in the direction of the arrow. The high-voltage diodes you will use in this experiment are color coded to indicate which way current flows: the dark end is the head of the arrow. Don't screw this up! It is important that you understand how the current flows in this experiment - if you get it wrong, your 1000 microfarad capacitor might blow up. When that happens, there will be a very loud pop, hot electrolyte will splash all over the place, and your cats will glare at you for being stupid. (Ask me how I know this...)

    Experiment 9: Click here for notes.

    Experiment 10: Click here for notes.

    Experiment 11: Click here for notes.

    Experiment 12: Click here for notes.

    Scott A Hughes.
    Last modified 20 March 2000.