I walked down the lab and I was standing outside by about 9.50am. I chatted to Dunc and Neil, and before long, we found ourselves in the physics lab.
Today it was the short experiments. Dunc and Neil teamed up with one another, so I found myself working with a guy called Tim Robinson. A nice guy and a capable physicist, but with unfortunate personal hygiene issues. Whenever he reached over to examine or adjust something I had to arrange to be elsewhere. It was not good.
The X-ray emitter, a crystal of sodium chloride, and the edge of the detector.
We worked through the morning on the X-ray diffraction experiment, which initially I was not wowed by, but I quickly became very absorbed in. In a way it bears some similiarities to the Compton long experiment. We did a speedy scan through the angles to find peaks of deflection, then took some finer measurements at 0.25 degree intervals to isolate the exact peak.
I found four peaks, three of which were due to one type of emission. There was apparently a further two peaks at least, I found one more but the energy was significantly weaker.
Having done this, I attempted to plot them on a graph, but the peak widths were so narrow that it made producing the graph difficult. Still, there was an interesting relationship in that the first peak was the highest, the second was less large and the third the shortest. I guess there must be a reason for this.
Using the exact location of the peaks and the known wavelength of the X-ray emissions, this enabled us to calculate the spacing between the sodium and chlorine ions, an amazing phenomenon. All three answers should be more or less the same, since they are talking about the same things. The first two were virtually identical, the third less so, but I had expected there would be a larger margin of error.
Having calculated that the distance between the ions was around 0.280 nanometres, I was keen to compare this with the 'accepted' figure - this turns out to be 0.282 nanometres.
To place a nanometre in context, there are 1,000,000,000 of them in a metre. Small!
Then after being given a couple of critical pieces of information, we were able to calculate the mass of a single 'cube' of sodium chloride (the sodium and the chlorine ions are arranged in a virtually perfect cubic structure). Knowing the mass, and having spent all day calculating the distance between the ions, this enabled us to calculate the density of the sample.
This turned out to be 2210 kg per cubic metre, within 2% of the accepted figure of 2165 kg per cubic metre. Very happy with that result!
Tim and I then moved onto the next 'short' experiment, concerned with measuring the speed of sound in air. This deceptively simple experiment is done in an interesting way. Using an oscilloscope to examine the wave of a pure note inside a tube (with a small speaker at one end, and a microphone at the other), we examined the way that moving the two closer or further apart caused the detected sound to shift in and out of phase with the original signal. By working out the distance needed to shift the sound a complete wavelength, this enabled us to compute the speed of sound - our figure was within 1% of the accepted figure.
Lissajous figures.
We switched the oscilloscope so that the timebase wasn't just a linear progression but used the detected sound as its input. Consequently, depending on the comparative amplitude and phase variance you get anything from diagonal lines to elipses. We examined the difference between the shapes generated when the signals were fully in phase, fully out of phase, and gradations inbetween.
This brought us neatly to 5.30pm.
Walked back up the damn hill and stood outside the dining hall, waiting for it to open.
I opted for a very competent chicken chasseur, and had a long and extremely pleasant conversation with Alex and Dave, about all sorts of things. It's the first time that I've taken an hour to finish dinner.
Alex and Dave, sharing a joke
Dave and Alex agreed to meet one another in the bar to talk about a Compton scattering equation that they were having difficulty with, and I said I would meet them. I rang home, and had a longer than expected chat with Alan, which was wonderful.
When I got to the bar, Dave was just leaving, to go to the guest lecture, given by one of our tutors, Nick Braithwaite. He's the one who sounds like a cross between Michael Parkinson and Peter Allis. I didn't really fancy this, so I stayed in the pub, and chatted with Alex for about an hour. He is a fascinating young man, and I very much hope that we stay in touch after the end of the course.
He lives in Budleigh Salterton, not a million miles away from my parents. Perhaps the next time we are down in that neck of the woods, Alan and I might call on him.
Alex bought me a pint (he rarely drinks; I admire his self-restraint!) and we chatted about subjects as varied as parenthood, religion, the OU, holidays, and school bullies.
I wanna take you to a Grey bar...
I resisted the temptation to buy a bottle of wine and take it back to my room. I have no intention of having a hangover in tomorrow's penultimate lab session, nor of being incapable of drinking alcohol for Thursday night's end of residential disco, which I believe is at Collingwood College next door.
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