Brad's Blog for Quarknet Workshop Summer 2008: July 14-18
From MariachiWiki
Monday July 14, 2008
The morning began with a great intro to the history of "what we know" about particle physics. I learned an interesting fact regarding Einstein's Theory of Relativity. Let me explain: Students constantly ask me the same question on each topic we cover throughout the school year. I usually have a good answer for this perpetual question, however, when we reach the topic of special relativity, the talk inevitably turns to the theory of time travel. While this is not (yet??) a practical application of Einstein's theory, it provide us with some fodder for interesting conversations at a time of the year when the weather outside is too beautiful to waste time in class with higher level learning. It turns out that the theory is used in everyday life in an application that most students are familiar with: GPS units. The 27 satellites orbiting our planet our planet send out signals that our hand held devices (more commonly our cell phones) use to calculate our location on earth. The timing of one satellites signal as received on the GPS unit compared to the timing of another signal from a different satellite is crucial for location purposes. Sycronizing the clocks on these satellites is one of the more difficult tasks. Since the satellites are traveling rather quickly (not sure how fast, 25,000 mphish??), their on-board clocks are subject to measurable effects of general relativity, namely that as speed increases, time SLOWS DOWN. The computers onboard the satellites are programmed to account for this time difference and thus account for the accuracy and precision of our GPS units. Very cool answer to the question "Why do we care about this stuff"?
In the afternoon, we built sound tubes and the necessary circuitry to run them. It was my first experience soldering and making circuits, which will be useful in the future.
Tuesday July 15, 2008
We spent most of the morning continuing with the construction of our sound tubes. Although they took nearly a full day ti build and test, they were worth the time. I was able to calculate the speed of sound to within a 1percent error. Very Cool!
In the afternoon we used the online oscilloscope and a telephone pic-up coil attached to our tablet computers through the microphone port. Another accurate measurement. Our percent error for calculating g was 0.3 percent!! here is a graph of our data below.
Here is the skinny on the lab
New twist to pendulum lab
Set up the weight on a pendulum clamp. Tape the small neo dynium magnet to the very bottom of the weight.
Place the telephone pickup coil (buy it at radio shack) under the pendulum on the table. A 5mm clearance between the magnet on the bob and the pick coil is good. Plug it into the microphone on the lap top. When the magnet passes over the coil, it will send a pulse to the computer.
Down load the oscilloscope software from the web site on the mariachi web. You will need to adjust the time and the amplitude on the screen to get a good signal. In order to measure the time, there is a button on the bottom labeled cursor. You can manipulate the cursor on the screen.
Oscilloscope software needs to be downloaded onto the computers ahead of time. Talk to the computer guys.
Wednesday, July 16, 2008
Today we got off to a quick start. We spent the morning building a circuit board that allowed us to illuminate a series of 6 LED lights. They ranged from color/wavelength IR 945nm, red 630nm, yellow 592nm, green 525nm, blue 470nm and UV400. Using a voltmeter and a series of switches, we read the threshold voltage required to turn the LED on. Using the formula eV=hf, we calculated h, Planck's constant. After graphing eV vs Frequency, I calculated Planck’s constant to within 0.75% error (that’s less than 1% !!!!) Very cool lab. This is something I can modify in the classroom as a lab exercise. It is especially useful since there are very few labs that I know of for modern physics. Great lab. See the final graph below of my data.
