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January 2014 Archives

Just a quick post to let you know that my attempts (struggles) with the 2013 Physics Scholarship exam are now freely available for all to make use of (laugh at). You can find them on Physics Lounge, http://www.physicslounge.org/scholarship-dr-marcus-wilson/ . A big thank you to Sam Hight for laying out the videos in an easy-to-use manner. 

I emphasize that there are no restrictions on their use - please download them, distribute them and use them as you wish.  

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Last year, Sam Hight and I made a collection of videos on tackling the 2012 Scholarship Physics exam. Well, to be precise, Sam did the videoing, editing, and distribution, and I just did the exam. The key thing, though, was that I did the exam 'live'. I was seeing the questions for the first time. I didn't give myself a few days to work out carefully composed and presented answers, like some of the slick model answers you find online. The idea was to give students an idea of what scholarship is like to do (answer: hard!)  but also how I think through a physics problem and come up with my solutions. Often what is lacking on a 'slick' model answer is any indication of how the writer 'knew' to tackle the question in the way she did. (Answer to that one - probably because she'd spend a few days looking at it, or wrote the exam question in the first place - neither terribly helpful to a student.)

By popular request, I did the same yesterday. Video camera in front of me, whiteboard, three hours with a scholarship paper. My conclusion? The 2013 paper was hard-as. (You can see for yourself here.) I'd rate it a good step up from the 2012 one. To be fair, different people have different strengths. It may have been that there was a 'bad' lot of questions for me in the 2013 paper, but it might have been a 'good' lot for someone else. I'd love to hear your thoughts on this one - do you think it's harder?

One thing I noticed was there was a lot of algebra and calculation in the 2013 paper, and there wasn't so much in 2012. The question about the A-frame ladder had a derivation involving three simultaneous equations to solve. But I got it! In the end. 

Sam and I will get the videos distributed in due course, probably via PhysicsLounge  http://physicslounge.org   If nothing else, you can watch me fumble around with a couple of questions which, 24 hours on, I realize weren't as difficult as I was trying to make them out. But if I showed you the answer today, it would be slick, and you'd be stuck wondering how I came up with it.  

Will they be helpful? You decide. If not, you can always have a good laugh at me squaring a number twice because I wasn't paying attention to what I'd written, and getting my notation in a muddle.  Whatever, I'd like to offer my congratulations to those who landed Scholarship Physics in 2013, because you most certainly deserve it!

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One of the great lines on the cult BBC show 'Red Dwarf' goes (approximately, from memory) like this:

Can't you go any faster, like so we're not being overtaken by stationary objects?

I'm sure my youngest sister would be able to correct the wording, and tell me immediately which episode it's from, who says it to whom (I think it's Rimmer to Kryten) and how many minutes and seconds it comes into the episode. Unfortunately (or maybe fortunately) I can't. But I've got the essence of it. 

The line is amusing because one can't possibly go so slow as to be overtaken by something stationary. If that is happening, you are going the wrong direction, and speeding up will only make matters worse.

But, in a sense, it can be true. I was reminded of this last weekend when we (Karen, Benjamin and I) went sailing with some of Karen's friends on lake Rotoiti (the one next to Rotorua). I haven't been sailing for ages. But lake sailing provides an easy re-introduction - it removes the need to think about tides as well as wind. I learnt to sail a long time ago on Portsmouth Harbour where tidal currents can be vicious indeed. You have to pay close attention to where you are actually going. You might be moving along nicely along the surface of the water, but if the water is heading at 4 knots in the wrong direction you have a problem. Your actual velocity (e.g. as a GPS would record) would be the vector summation of your velocity relative to the water, plus the velocity of the water. The first might be just great [and you'll experience the exhilaration of the boat cutting through the water nicely, leaving bits of driftwood and plastic bottles (it is Portsmouth, after all) in its wake] . But the second could push you way off course. When you've got little wind it can become impossible to get where you want to be. 

Then you really can be overtaken by stationary objects. There's nothing quite like the feeling of being out on the harbour at the end of a summer's day, when the sea breeze suddenly dies, and finding yourself being overtaken by a stationary buoy. At that point, grabbing hold of the buoy can be a good idea.

I am informed by someone with reasonable knowledge of the region that the 'Round the Island Race' (round the Isle of Wight)  has been won on occasion by anchoring. (Obviously not for the entire race.) In other words, being stationary is as fast as you can possibly go. 

 

 

 

 

 

 

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Physicists and engineers have a particular fondness for using symbols for things. Thus, the speed of light becomes 'c'. Planck's constant is 'h'. And so forth. Not content with the latin alphabet, they have commandeered the greek one too: The Stefan-Bolztmann constant is  'sigma', the permittivity of free space is epsilon0 (the greek letter epsilon with a subscript zero) and so forth. 

It comes as no surprise that even those two alphabets aren't sufficient. While mathematicians resort to using the Hebrew alphabet to allow for more possibilities, physicists take the approach of using the same symbol to mean different things. So, for example, 'k' is used for spring constant, Boltzmann's constant, wavenumber and so on. Usually this causes no ambiguity - spring constants are used for describing the stiffness of springs, Boltzmann's constant in used in thermodynamics to relate temperature to energy, and the wavenumber is used to describe wave phenomena. Occasionally we might need to use Boltzmann's constant and wavenumber at the same time, though when we do which is which is generally fairly obvious. It's just like language - one word might have multiple meanings, and mostly we don't get confused. 

Just occasionally, however, we run into trouble. I've been preparing some notes for our third-year Electromagnetic Waves paper. It's a paper that is taken by a combination of engineering students and physics students. I'm a physicist, but most of the students are engineering students, and the textbook that the paper draws heavily from is an electronic engineering textbook. While there is a great deal of overlap between the two disciplines, there are also clashes. I ran into trouble over terminology a couple of years ago in a mechanical engineering paper - you can read about that here. Now, in the Electromagnetic Waves paper, we have the greek symbol 'delta' being used for two very much related things.

Electromagnetic waves don't go through good conductors at all well. The energy is taken from the wave very quickly. A parameter used to describe how quickly is known as the 'skin-depth' (and here) (it's roughly the distance that the wave will penetrate to), and is conventionally given the greek letter 'delta'. That's the physics part. What do we mean by a 'good' conductor? We can characterize how conductive a material is, relative to the frequency of the wave (which is what matters for determining the depth of penetration) by something known to electronic engineers as the 'loss tangent'.  That's given the notation 'tan delta' - the tangent of delta. Unfortunately delta and delta are not the same thing, but are very much related to each other. Confused? Poor students. 

It's true that the most able students don't tend to have an issue with this, but this kind of thing can really trip up the less able ones. When one is familiar with their use, it still is pretty easy to distinguish them, as it is in spoken language, when one knows the language.  Which brings me to Benjamin. He demonstrates some very interesting word usage. "Dadda" is used to mean "Daddy", "Lawnmower" and "Aeroplane".  Illogical? Actually, no. "Dadda", to mean "Daddy", was, as is the case for many children, his first word. Daddy does the lawnmowing - the lawnmower doesn't move without Daddy on the end of it. Therefore "Dadda" was also carried over to mean "Lawnmower". And, more recently, he's become very aware of planes in the sky. They sound rather like lawnmowers. Hence "Dadda" now also means "aeroplane". Even a picture of an aeroplane in a book is a "Dadda". So, when we're out in the garden and Benjamin shouts "Dadda dadda dadda" it is not necessarily because he wants my attention. Confusing. Sometimes, even for me, yes.

More curious than that, however, is the term "Ya-ya". This is truly complex, and I'm sure would fascinate linguists. It means, amongst other things "Mummy" and "Rabbit"; sometimes both at once. 

 

 

 

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The UK's Institute of Physics has just released a report "Closing doors: exploring gender and subject choice at schools" It follows on from the report a year or so back: "It's different for girls", which looked at the way girls experienced physics. I blogged about the latter report here

The report is not long, so you can read it in full. Although the results are, for the most part, not at all surprising, it is still good that they've been properly researched and are based on evidence, rather than anecdote. That should provide a firmer basis for doing something about the problem. 

Essentially, the study looked at six different subjects at 'A'-level (taken at the end of school at about age 18): Biology, English, Psychology, Physics (of course), Economics and Mathematics. These subjects were chosen as they cover the spectrum of different subjects at A-level, both core ones, popular choice ones and less popular choice subjects. English and Psychology have a fairly strong bias female bias (in terms of the numbers of students taking them), biology is almost gender-balanced, economics and mathematics have a fairly strong male bias, whereas physics has an extremely strong male bias: 80% of students taking physics A-level are male. 

The study analyzed data from ALL co-ed secondary schools (state and independent) in England, from 2010-2012, though schools where numbers doing A-level were very small were omitted. It's a comprehensive study!

There are some interesting results. First, independent schools do better at tackling gender inbalance than state schools. (There are relatively few co-ed independent secondary schools so the statistics are more uncertain).  Then, some regions do much better than others, but it's not down to socio-economic reasons. The reasons for regional discrepancies need investigation. 

Next, there's notable differences between schools with and without their own 'sixth-form'. Some secondary schools have 'sixth-forms' attached, whereas students at other schools need to move to a sixth-form college to do A-levels. Students who need to move end up making more gender-specific subject choices that those who don't. Perhaps this is suggestive that being able to see other people of your sex tackling a subject in the years ahead of you will encourage you to do it. This result was also found in the 'It's different for girls' study.

Finally, there's an interesting observation regarding subject choices. Boys, as a cohort, are quite broad in their choices of A-level subject. A boy is, roughly speaking, equally likely to choose to study physics, chemistry or biology. However, the choices of girls are much more polarized - some subjects are highly attractive, and some (like physics) are highly unattractive. The implication I draw from that is that it is the choices that girls make (rather than the choices that boys make) that leads to the gender imbalances. A conclusion would therefore be that efforts to correct gender imbalances should be actively focused towards girls. 

A further, physics-specific conclusion can be drawn regarding the low numbers of students taking physics A-level, in general: it is caused by a lack of girls, rather than a lack of boys. The implication is that encouraging girls to take physics won't just help gender balance, but will help tackle the problem of low student numbers in general - it will, probably, increase female participation but also without reducing male participation. That is of relevance to university, where many institutions (such as The University of Waikato) struggle to attract students to physics. 

Finally, I'll point out that when I did my blog entry on 'It's different for girls' I got some flak for using the word 'girl' rather than the word 'woman'.  In using the word 'girl' here (or, for that matter, boy), I am referring to a child at school. I note that here, in Hamilton, we have a 'Hamilton Girls' School' and a 'Hamilton Boys' School'. The choice of words 'girl' and 'boy' mirror the choice used in the two IoP reports. 

 

 

 

 

 

 

 

 

 

 

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I started back at work on Monday thinking that it would be a nice, peaceful day, with no-one else around on campus. Surely, on a beautiful, sunny, 6th January, the entire of Hamilton except for myself would be on the beach at Raglan. Wow, was I mistaken. The campus was buzzing with activity and there was a constant stream of knocks on my door from people wanting things done. I've hardly had time to breathe, let alone write blog entries. Maybe things will quieten down when A-semester starts (!). 

On Sunday Benjamin (now 18 months old) acquired a balloon filled with helium. I've been wondering for a little while about letting him drop a helium balloon just to see the reaction when it fails to hit the floor, and I was given the chance when a friend gave us one. (Inidentally, the frivolous use of helium in party balloons is a subject that is worth debating in itself.) Our child was most impressed and rather excited to see that not everything obeys the law of gravity, or, at least, not in the way  he understood it. 

So, the balloon was up on the ceiling for a few hours. What surprised me, however, was how quickly it lost its helium. The following morning it was back on the floor, rather deflated. This probably shouldn't have surprised me - there's good reason that the helium escapes the balloon quickly - the helium atoms in the gas are very small, and very inert (non reactive). They can simply make their way out through very tiny holes in the rubber of the balloon. If the balloon were filled with air (about four fifths nitrogen molecules - two atoms of nitrogen joined together, and one fifth oxygen molecules) I'd expect it to stay inflated rather longer. The air molecules are so much larger than the helium atoms. 

Defining the size of an atom is a bit like defining the size of Auckland. Putting aside artifially drawn boundaries, where exactly does the urban development stop? Nonetheless, there are some practical definitions of atomic size. Helium has a diameter of about 60 picometres (1 picometre is ten to the power of minus 12 metres, that is, 0.000 000 000 001 of a metre). Contrast this to the size of a nitrogen molecule, which is (again, vaguely), about 100 picometres wide. The smaller helium is simply better at getting out through the holes in the rubber balloon, and so the thing doesn't stay inflated for long. Instead, some precious atoms are lost into the upper atmosphere.  

 

 

 

 

 

 

 

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