Saturday, March 31, 2007

Magnetism: Ferro, Para, Dia

FERRO | Ferromagnetism is the "normal" form of magnetism which most people are familiar with, as exhibited in horseshoe magnets and refrigerator magnets, for instance. It is responsible for most of the magnetic behavior encountered in everyday life. The attraction between a magnet and ferromagnetic material is "the quality of magnetism first apparent to the ancient world, and to us today," according to a classic text on ferromagnetism. Ferromagnetism is defined as the phenomenon by which materials, such as iron, in an external magnetic field become magnetized and remain magnetized for a period after the material is no longer in the field. All permanent magnets are either ferromagnetic or ferrimagnetic, as are the metals that are noticeably attracted to them.

No interesting video clip to show. Just find your own magnet!

PARA | Paramagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field. Paramagnetic materials are attracted to magnetic fields, hence have a relative magnetic permeability greater than unity (or, equivalently, a positive magnetic susceptibility). However, unlike ferromagnets which are also attracted to magnetic fields, paramagnets do not retain any magnetisation in the absence of an externally applied magnetic field.

Elements/compounds could be paramagnetic if they have unpaired electrons. The following are some examples of paramagnetic elements:

Aluminium Al [13] (metal)
Barium Ba [56] (metal)
Oxygen. O [8] (non-metal)
Platinum Pt [78] (metal)
Sodium Na [11] (metal)
Strontium Sr [38] (metal)
Uranium U [92] (metal)
Technetium Tc [43] (artificial)


Many salts of the d and f transitional metal group show paramagnetic behaviour. Examples are:

Copper sulphate
Dysprosium oxide
Ferric chloride
Ferric oxide
Holmium oxide
Manganese chloride

The below video clip shows a liquid oxygen bridge suspended by a strong u-shaped magnet. This demonstrates the fact that magnetic force > gravitational force.

DIA | "This is a live frog. An object does not need to be superconducting to levitate. Normal things, even humans, can do it as well, if placed in a strong magnetic field. Although the majority of ordinary materials, such as wood or plastic, seem to be non-magnetic, they, too, expel a very small portion (0.00001) of an applied magnetic field, i.e. exhibit very weak diamagnetism. The molecular magnetism is very weak (millions times weaker than ferromagnetism) and usually remains unnoticed in everyday life, thereby producing the wrong impression that materials around us are mainly nonmagnetic. But they are all magnetic. It is just that magnetic fields required to levitate all these "nonmagnetic" materials have to be approximately 100 times larger than for the case of, say, superconductors. This experiment was conducted at the Nijmegen High Field Magnet Laboratory."

A large black superconducting disk was cooled with liquid nitrogen. When the disk goes into the superconducting state it expels magnetic field. This is called perfect diamagnetism. If you place a magnet above the disk when it is superconducting then it will levitate. This is known as the Meissner effect.

[99% Wikipedia and YouTube.]

Friday, March 30, 2007

Chemistry degrees

Emily Wilson
Friday February 16, 2007

"It is 9am on a Monday morning and 60 or so third-year chemistry students are already in their seats, files and pencil cases at the ready. Dr Chris Russell - young and dressed in a brown-striped shirt and chinos - will be our guide to inorganic chemistry for the next 50 minutes. And he's off, chalk flying!

Russell talks about "planar ML3 and ML2 fragments", "ligands" and "non-bonding orbitals" with clarity and enthusiasm. It is all entirely familiar to me - and yet utter gobbledegook.

Russell draws pretty, floaty diagrams on the blackboard with Ls and Ms and dots. L must stand for "ligand", whatever that is. But M? There is a periodic table on a wall of the lecture hall, but there is no M on it. Then Russell mentions "transitional metal chemistry", and the truth dawns: M stands for "metal", and I am, by any measure, the dumbest person in the room.

I studied at Bristol's school of chemistry from 1988 to 1991. I chose chemistry for a bunch of non-reasons - it was like, you know, one of my A-levels, and I was like, 18, and did not have a clue what I wanted to do with my life. In the event, it proved to be the exact opposite of a doss: both difficult and staggeringly time-consuming. It was a 9-to-5 business, five days a week.

Back in my day, the course was divided into three disciplines: copying, swotting and lab survival. In lectures there was no time for comprehension: our task was to accurately copy down reams of scribbled diagrams and equations from the blackboard. If you skipped a lecture, it would take at least 50 minutes to copy someone else's notes, and then you could never be sure that they hadn't made some awful error. (I wonder now why we never used a photocopier, but then this was at a time when undergraduates had no access to computers: I saw my first one two years after leaving university.)

Then there was the swotting: revising for exams became the time when you had to make sense of your notes, and that took out months of our lives. And finally there were the labs, where we spent our afternoons - a quite literally explosive mixture of deadly chemicals, teetering glassware, open flames and blind panic. It was all deeply Victorian, and we work-shy children of the 1970s were made to feel like proper no-marks most of the time.

University science is now in real crisis - particularly the non-telegenic, non-ology bits of it such as chemistry. Since 1996, 28 universities have stopped offering chemistry degrees, according to the Royal Society of Chemistry.

The society predicts that as few as six departments (those at Oxford, Durham, Cambridge, Imperial, UCL, and Bristol) could remain open by 2014. Most recently, Exeter University closed down its chemistry department, blaming it on "market forces", and Bristol took in some of the refugees.

The closures have been blamed on a fall in student applications, but money is a factor: chemistry degrees are expensive to provide - compared with English, for example - and some scientists say that the way the government concentrates research funding on a small number of top departments, such as Bristol, exacerbates the problem. The upshot is that Britain is turning out fewer and fewer chemists - even though there are jobs for them. Against this backdrop, it seems quite important that chemistry teaching is making an attempt to pull itself into the present; that it is as engaging as it can be; that it is no longer quite the dusty experience that it was in the early 90s.

Back in lecture theatre two, Russell is talking about "delta symmetry orbitals". You can see that he cares. He is one of the most popular lecturers here, the students tell me later.

All these students, I realise, have arrived with the notes for this lecture already in their possession - printed out from a website that also provides them with sample exam questions and workshop material. Their only job here is to annotate their notes if asked to. What a brilliant leap forward. The death of the science of copying. Later, a professor tells me that the real problem now is to keep the students' attention for the full 50 minutes.

Suddenly, a word that normal people and even journalists have heard of ... "Polonium is named after Poland," says Russell. "But that's by the way," he adds. We're back to ligands.

At 10am I have a physical chemistry tutorial with three first-year students. We sit around a little table. The students seem very young, and sweet, the bloom still fresh on them. Professor Andrew Orr-Ewing is quietly spoken, calm and super-clear. We work through a set of questions that cover the "particle in a box theory" and "tunneling effects". I sit frozen with terror, in case Orr-Ewing asks me a question and it becomes clear that I have forgotten everything I learned here. When he asks the students questions, I flinch for them, but they seem to know their stuff . There is no way I would have been so sharp in my first year here - what has happened to undergraduates?

Lisette Voûte is 21 and a third year; she is doing a four-year version of the course and will emerge next year with an MSci. She is of the opinion that chemistry's rigours are an excellent foundation for life, and says, "It's a great degree to have."

She is positive about the way it is taught, and says you can now complain if lecturers are rubbish. But then Voûte went into this knowing what she would be up against, and she knows what she wants to do at the end of it: she is the exact opposite of the hopelessness that was me at 21. Maybe all those debts and top-up fees have made students more wised-up. Then I meet another student, who asks not to be named. Why did he do chemistry? He is not sure. Does he like it? No - it is "baffling", and if he'd had any idea how hard it would be, he wouldn't have done it. What will he do next? He doesn't know. This could be me, 16 years ago. "But these are meant to be the best years of your life, right?" he says.

"God no!" I say. "I was miserable at university. I made a mess of everything. My private life was a car crash. I didn't like my course. I felt totally useless. Of course I'm a million times happier now!" He looks at me - an ancient person, on the verge of Zimmer-dom - and I can see that he is not convinced.

Later, when I meet up with my former organic chemistry lecturer, Dr Lionel Hart, I ask him if students have changed since he first started teaching? "No, not at all," he says. "They're just the same."

Bristol's school of chemistry, once a monument to 60s concrete, has had a face-lift since my time here - from the outside, it looks less like a Doctor Who set than it did. There is a new reception area. And the department has just been fitted out with state-of-the-art labs - though it turns out that even the old labs are pretty fancy these days. Someone has decided that wooden benches encrusted with decades' worth of toxins are not a brilliant idea in a human-rich setting, and they have all been replaced with gleaming white counters and computers. Lab specs have changed too. Out go the NHS clear plastic ones, in come bendy ones with blue piping. The labs still stink of solvents though - which really can't be a good thing.

Meanwhile Dr Paul Wyatt, the director of undergraduate studies, has come up with a computer programme that will soon allow undergraduates to practise experiments in a virtual setting before they get into the lab. This will be another big step forward - especially as doing your experiments first on the computer will be heavily compulsory.

It will still be lab though. And it will still be really hard. On the train home, it occurs to me that perhaps the building blocks of chemistry are, necessarily, inescapably hard and dry. However many computer tricks they come up with, however shiny the labs, perhaps undergraduate chemistry is simply un-sex-uppable. There is stuff you need to learn if you are going to be a chemist, and there is a lot of it, and it is difficult. And that's the deal, even though, these days, that is not the sort of deal people relish. Perhaps only Voûte's view - that courses such as chemistry are "good" degrees to have - can save us from becoming a nation with no idea what an atom is."


Thursday, March 29, 2007

Tuesday, March 27, 2007

Tasty (?) Conversion

2000 pounds of Chinese soup = Won ton

Tuesday, March 20, 2007

Why base 10?

Have you ever wondered why we chose base 10 for our number system? E.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 etc. and not 0, 1, 2, 10, 11, 12... (base 3).

Obviously, because we have 10 fingers. But that's kind of selfish of us - and should I also say not very mathematical. Tens do not occur often in nature anyways - it just so happens that we have 10 fingers.

Interestingly, before base 10 was universally used, base 11, 12, and 20 have been used. This is shown in our languages. E.g. eleven, twelve, as opposed to oneteen, twoteen; or vingt and quatre-vingt in french.

Base 2 is singled out as the one with the smallest possible base. Only digits 1 and 0 are used. Every other number could be represented by 1's and 0's. So that 1 + 1 = 10 and 1 * 1 = 1. The obvious disadvantage of this binary system is that long expressions are needed to represent even small numbers. E.g. 79 is expressed as 1001111, which is really 7*10^1 + 9*10^0 = 1*2^6 + 0*2^5 + 0*2^4 + 1*2^3 + 1*2^2 + 1*2^1 + 1*2^0. But multiplication is very easy. And other possible problems may also be easily solved with binary. Is this what God uses?

Sunday, March 04, 2007

American view?

Is this how americans view the world?

I don't mind, I don't know much of the world myself. But spell the elements of the periodic table right!