On the way home

Woke up feeling surprisingly good, given how late a night I had last night. I apparently stayed about three hours longer than the first time I said I was intending to go to bed!

I went for breakfast at about 8.10am, and found the dining hall to be quite full. Had a full cooked breakfast, then dashed back to the room, rang Alan at 8.30am as usual, and managed to multitask, finishing the packing at the same time. Bye bye room 23, you served me well, despite what I thought of you at the beginning of the week.

I took my key to Grey reception and gave it back, then took my cases and jacket to The Old Library, a room set aside as a storage room for us.

Feeling strangely empty, I walked down to the physics lab for the last time. I was early, almost nobody else was around. I got to the lab and made an early start on the theory of the Helmholtz coils. In a nutshell, the idea is that by having two coils parallel to each other with current run through each, there is a point midway between them where the magnetic field lines sun straight and parallel to the coils. Lots of pretty hard algebra!

We applied a charge to the electron gun, which produced a nice clear beam of electrons vertically downwards. We then looked at the effect of a each pole of a simple bar magnet on the direction of the beam. Both poles repelled the beam but each in opposite directions.

We then looked at changing the voltage and current so that the beam was deflected to the extent that it curled around the gas tube and back on itself, ie producing a circle.

Having done this, we speculated (then tested) what the effect would be in increasing the voltage, then the current. We discovered that increasing the voltage increases the radius of the beam circle, and that increasing the current decreases it.

Afterwards we varied the voltage from about 150 volts, up to 250, but for each voltage then adjusted the current so that the beam circle remained the same size.

This was not difficult but technically very awkward. It was obvious that the uncertainties in current and voltage were insignificant compared to the error in the measurement of the circle, since this was being done completely by eye.

We did a complete set of measurements where I adjusted the current - a feat which required Neil to guide me to the correct control, as in order see the beam, you have to cover yourself with a black cloth.

David Keen said, quite loudly, "ask your lab partner to put your hand on the knob." Accurate and very funny. He has been master of the single entendre this week.

I found making the measurements rather subjective, and it was very clear that my figures were not going to be good. However we had the luxury of time on our hands, and to get a better result, we repeated all the readings but with Neil under the cloth, and me guiding his hand to the right knob. It was quickly obvious that Neil's readings were significantly better, so we took the wholly reasonable decision to use his readings rather than mine.

This decision was vindicated when we plotted the current-squared against the voltage on Excel. Mine looked like a meandering river trying not to go in a straight line, Neil's data was dead straight.

Some complex algebra followed, which enabled us to work out a constant for that particular coils configuration. We applied this in a further formula, giving us the electron charge to mass ratio.
Despite doing our measurements on relatively simple equipment, it was deeply gratifying to get a result not only in the correct order of magnitude, but with the 'accepted' value within our margin of error.

Neil was an excellent lab partner and an accomplished physicist. his grasp of the algebra and vector manipulation were both great, and he kept me on the straight and narrow.

We had a long talk about the fact that I had re-taken the course after failing it. Neil was very encouraging and said it showed a real strength of character. I thought this was quite a compliment. The two of us had a good conversation with David Keen about the experiment, the week as a whole, his PhD thesis, and a few other things.

Once all the groups had reported in, David said a few words and awarded the 'Thomson Trophy' to the best pair, which was Duncan and Tim. The trophy was in fact a polystyrene cup with a printed label! Very funny. That brought the lab to an end, and also marked the end of all the lab work.

Walked back up the damn hill to Grey, and had the final lunch. I opted for fish, skipped the chips but had some beans. I really needed some carbohydrates in me, my system has not been pleased in the change in culinary routine, and it's been difficult to attend a morning toilet at all let alone a regular one.

Lunch was a very leisurely affair, as we had all checked out of the rooms, and hence couldn't really go anywhere. I had a yogurt for desert, as the regular desert choice had chocolate in it, and someone brought me a cup of coffee, which turned out to be magnificent coffee. A pity I didn't discover this sooner!

After a nice leisurely lunch, Dunc, Alex, Neil and I walked up to Holgate House, and sat in good seats for the final debrief.

David was extremely funny throughout, and made a reference to people having a good night on the tiles last night - a thinly veiled reference to Patrick's unfortunate incident last night when he damaged several ceiling tiles and caused a few to fall to the ground, whilst he was on top of the vending machine. Silly boy.

David also handed out a few prizes to people, which was good, showed some photos from the Tuesday boat race ("otherwise known as Fear on the Wear"), then talked about the TMA fairly extensively.

I am in luck this year, the topic of the main write up, worth fifty percent of the marks, is on the magnetic fields lab work, the very set of experiments that we finished today. Very good result for me. David finished with a daft song sung by all the tutors, and he accompanied on his guitar ("And it's all too much for the poor student to bear"). Great fun.


After collecting a copy of the TMA and some graph paper, it was time to leave. Many handshakes. Felt rather sad to be going. Tom Wilks gave me a heartfelt handshake and a goodbye. He is a great tutor and a thoroughly decent guy.

Said a sad farewell to Duncan and Alex, then went to reception, to see if they could call a taxi for me. To be honest I didn't feel like waiting fifteen minutes or like sharing it, so I took the decision to walk from Grey to the railway station, alone with my thoughts. About a hundred yards ahead, I could just see Alex walking in to town (he has plenty of time to kill until his flight at eight tonight).

Wheeling a suitcase, a hand luggage case and a carrier bag full of stuff turned out to be something of an endurance, and I arrived at the station sweating and swearing.

There were loads of fellow OU students at the station. After buying a couple of drinks to rehydrate myself, I sat on the platform, texted Alan whilst I waited for my train.

Farewell Durham, it's been an amazing week, and I have loved it all. I will smash this TMA and get the very best score I can.