Archive for Physics

R.I.P. Phil Anderson (1923-2020)

Posted in Uncategorized with tags , , on March 30, 2020 by telescoper

I heard this morning via a friend who knew him personally of the death, yesterday at the age of 96, of condensed matter physicist and Nobel Laureate Professor Philip Warren Anderson. He will perhaps be best remembered known for Anderson Localization but he worked on a huge range of topics in physics and his influence was felt across many branches of science (including astrophysics). It’s too early for obituaries to have been published yet but I will add links when they become available.

Update: here is the New York Times obituary.

R.I.P. Philip W Anderson (1923-2020).

From the Inventor of the H-index

Posted in Biographical, The Universe and Stuff with tags , , , , on March 5, 2020 by telescoper

My third-year students are busily engaged with a Computational Physics class test so I thought I’d occupy myself for a few minutes by sharing an interesting little paper that appeared on the arXiv a few weeks ago. The paper is by Jorge Hirsch, the inventor of the (in)famous H-index.

Here is the abstract:

A magnetic field H is expelled from the interior of a metal becoming superconducting. Everybody thinks the phenomenon is perfectly well understood, particularly scientists with the highest H-index think that. I don’t. I will explain why I believe that without Holes, conceptualized by Heisenberg in 1931 fifty years after Hall had first detected them in some metals, neither magnetic field expulsion nor anything else about superconductivity can be understood. I have been a Heretic in the field of superconductivity for over 30 years, and believe that Hans’ little story about the emperor perfectly captures the essence of the situation. Here is (a highly condensed version of) the wHole story.

You will see that, despite the liberal sprinkling of letters H, the paper isn’t ostensibly about the H-index, but it does contain some interesting comments thereon, including:

I proposed the H-index hoping it would be an objective measure of scientific achievement. By and large, I think this is believed to be the case. But I have now come to believe that it can also fail spectacularly and have severe unintended negative consequences. I can understand how the sorcerer’s apprentice must have felt.

I think the opinion of a scientist about the value of the H-index roughly speaking divides according to whether a said scientist has a big one or a small one. Those lucky enough to have a high H-index probably think it is fine, while those who have a low value can probably find a reason why it is flawed. My own H-index (42 according to Google Scholar) is mediocre, which I reckon is a fair reflection of my status.

A Problem of Snooker

Posted in Cute Problems, The Universe and Stuff with tags , , , on February 25, 2020 by telescoper

I came across the following question in a first-year physics examination from Cambridge (Part 1A Natural Sciences) and, since I have posted anything in the Cute Problems folder for a while I thought I would share it here:

Answers through the comments box please! And please show your working!

P.S. The preamble does not say whether you can also assume irrelevant formulae without proof…

 

The Reverend Professor Callan

Posted in Biographical, History, Maynooth, The Universe and Stuff with tags , , , , , on February 5, 2020 by telescoper

I’ve had a busy day doing various things that took me to various places on the Maynooth University campus, culminating in my first visit to the Department of Mathematics and Statistics (which is based in Logic House) to give a colloquium. On my travels I passed this sign, which I hadn’t noticed before:

Since I’ve been too busy to write a post today I thought I’d rehash an old one about the person named in the plaque, which is above Callan Hall (on the South Campus)

Father Nicholas Callan (or, more formally, The Reverend Professor Nicholas Joseph Callan) was born in County Louth in 1799 went to the seminary of St Patrick’s College, Maynooth, in 1816 to train as a priest. During his time as a seminarian Callan studied ‘Natural Philosophy’ and became interested in experiments involving electricity. In 1823 Callan was ordained as a priest, and went to Rome in 1826 to obtain his doctorate in Divinity. At the time Italy was a centre for research into electricity and here Callan became familiar with the work of the Italian physicist Alessandro Volta who had developed the world’s first battery. Callan returned to Maynooth where he was made chair of Natural Philosophy, a post he would hold until his death in 1864.

Callan is most famous for inventing the induction coil (in 1836). By connecting two copper wire coils to a battery and electromagnet and then interrupting the current he was able to generate much larger voltages than could be obtained from batteries alone. His 1837 version that used a clock mechanism to interrupt the current 20 times a second is estimated to have produced 60,000 volts – the largest artificially generated charge at that time. It is said that his induction coil could produce sparks 15″ long, which must have been fun to watch.

Callan’s biggest induction coil, unfinished at the time of his death, can be found in the National Science Museum of Ireland (which is in Maynooth). This was one of the largest in the world at the time. The iron core is 109 cm long. The secondary windings are 53 cm in diameter and consist of about 50 km of iron wire insulated with beeswax. They were made in three separate rings separated by air gaps, so wires carrying large voltage differences would not lie adjacent to each other, reducing the risk of the insulation breaking down. At the left end is a vibrating mercury ‘contact breaker’ in the primary circuit, actuated by the magnetic field in the primary, which interrupted the primary current to generate potentials of over 200,000 volts.

Sadly Callan’s work was forgotten for quite a period after his death – experimental electromagnetism was not a priority for St Patrick’s College at this time – for which reason the invention of the induction coil has often been attributed to Heinrich Ruhmkorff who made his first device (independently) about 15 years after Callan. More recently, however, Callan’s achievements have been more widely recognized and in 2000 the Irish government issued a stamp in his honour.

The Callan Building

Nicholas Callan was laid to rest in the College Cemetery at Maynooth in 1864. The Callan Building (above) on the North Campus of the present-day Maynooth University is named in his honour, as of course is Callan Hall which I mentioned at the start.

Spring Semester Starts

Posted in Biographical, Education, Maynooth with tags , , , , , , on February 3, 2020 by telescoper

It’s February 3rd 2020, which means that today is two days after Imbolc, a Gaelic festival marking the point halfway between the winter solstice and vernal equinox. The 1st Day of February is also the Feast day of St Brigid of Kildare (c. 451-525), one of Ireland’s patron saints along with Saints Patrick and Colm Cille. One of her miraculous powers was the ability to change water into ale, which perhaps explains her enduring popularity among the Irish.

In Ireland this day is sometimes regarded as the first day of spring, as it is roughly the time when the first spring lambs are born. It corresponds to the Welsh Gŵyl Fair y Canhwyllau and is also known as the `Cross Quarter Day’ or (my favourite) `The Quickening of the Year’.

Today is, appropriately enough in the light of all this, the start of the Spring Semester of teaching at Maynooth University, the third Spring Semester I will have experienced here. The weather has even played along; it has definitely been spring-like. The Campus, whicgh has beenhas been very quiet for the last week or so since the examinations finished, is full of students again.

This Semester, as was the case last year, I am teaching Engineering Mathematics II and Computational Physics I. The former, what you would probably call a `service course’, covers a mixture of things, mainly Linear Algebra but with some other bits thrown in for fun, such as Laplace transforms. Interestingly I find the Mathematical Physics students do not encounter Laplace Transforms in the first year, but perhaps engineers use them more often than physicists do? I think I’ve written only one paper that made use of a Laplace transform. Anyway, I have to start with this topic as the students need some knowledge of it for some other module they’re taking this semester. I reckon six lectures will be enough to give them what they need. That’s two weeks of lectures, there being three lectures a week for this module.

Once again my teaching timetable for this module is quite nice. I have lectures on Monday, Tuesday and Wednesday and then the students have a choice of tutorial (on either Thursday or Friday). That means I can get through a decent amount of material each week before each tutorial. I don’t do the tutorials, by the way: that’s left to one of our PhD students, who gets paid for doing that and correcting the weekly coursework. There are about 50 students on this module, divided into two courses: Electronic Engineering and Robotics and Intelligent Devices. We don’t have Civil or Mechanical or Chemical Engineering, etc at Maynooth, in case you were wondering.

Anyway, my first lecture was this afternoon at 2pm and had a good turnout. It was so sunny outside that we had to close all the blinds. That’s quite an unusual event for a February lecture!

My first Computational Physics lecture is on Thursday, after which it will be back to the Department for some frantic behind-the-scenes activity ahead of the afternoon lab session, which is in a computer room near my office. Students attend one two-hour lab session in addition to the lecture, on either Thursday or Tuesday. The first lecture being on Thursday the first lab session will be Thursday afternoon, with the same material being covered the following Tuesday.

While my teaching duties are the same this year as they were in the corresponding semester last year, there is a significant difference this year in that I am now also Head of Department. Either side of my first lecture I had to attend a meeting of the Faculty Executive for Science & Engineering, a meeting on `Project LEGO’ (which, sadly, did not involve any actual Lego but was instead about the proposed redesign of the University’s website) and a meeting of Academic Council. I have also been trying to sort out tutors and tutorials for the forthcoming Semester: these don’t start until next week so there’s time, but it’s quite a challenge to get everyone sorted out. A few timetable clashes have also come to light. So, in summary, I’m a bit worn out after today and will shortly go home to vegetate.

At least I didn’t have to find time for the regular Monday afternoon Euclid telecon in which I usually participate. There wasn’t one today because the working group of which I am part is actually meeting in person for a few days… in Paris! I couldn’t go because of all the above!

Yet another easy physics problem…

Posted in Cute Problems with tags , , , on December 2, 2019 by telescoper

Last week I posted a little physics problem that generated a large amount of traffic (at least by the standards of this blog), so I thought I’d try another one.

The examination comprised two papers in those days (and a practical exam); one paper had long questions, similar to the questions we set in university examinations these days, and the other consisted of short questions in a multiple-choice format. This question is one of the latter. Incientally, for those of you who have asked, the multiple-choice examination contained 50 such questions to be answered in 2½ hours, which is three minutes per question.

(You can assume that the acceleration due to gravity is 9.8 ms-2.)

And here is a poll in which you may select your answer:

Comments on or criticisms of the question are welcome through the comments box…

Another easy physics problem…

Posted in Cute Problems, The Universe and Stuff with tags , , , on November 26, 2019 by telescoper

Many moons ago I posted an `easy’ physics problem from the Physics A-level paper I took in 1981. The examination comprised two papers in those days (and a practical exam); one paper had long questions, similar to the questions we set in university examinations these days, and the other consisted of short questions in a multiple-choice format. The question I posted was one of the latter type. I was reminded about it recently because, years on, it appears people are still trying it (and getting it wrong).

Anyway, since I’m teaching similar things to my first-year Mathematical Physics class I thought I’d put up another question from the same paper.

And here is a poll in which you may select your answer:

Comments on or criticisms of the question are welcome through the comments box…