Category Archives: Teaching

Remembering Stephen Hawking

Like many physicists, I woke to some sad news early last Wednesday morning, and to a phoneful of requests from journalists for a soundbyte. In fact, although I bumped into Stephen at various conferences, I only had one significant meeting with him – he was intrigued by my research group’s discovery that Einstein once attempted a steady-state model of the universe. It was a slightly scary but very funny meeting during which his famous sense of humour was fully at play.

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Yours truly talking steady-state cosmology with Stephen Hawking

I recalled the incident in a radio interview with RTE Radio 1 on Wednesday. As I say in the piece, the first words that appeared on Stephen’s screen were “I knew..” My heart sank as I assumed he was about to say “I knew about that manuscript“. But when I had recovered sufficiently to look again, what Stephen was actually saying was “I knew ..your father”. Phew! You can find the podcast here.

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Hawking in conversation with my late father (LHS) and with Ernest Walton (RHS)

RTE TV had a very nice obituary on the Six One News, I have a cameo appearence a few minutes into the piece here.

In my view, few could question Hawking’s brilliant contributions to physics, or his outstanding contribution to the public awareness of science. His legacy also includes the presence of many brilliant young physicists at the University of Cambridge today. However, as I point out in a letter in today’s Irish Times, had Hawking lived in Ireland, he probably would have found it very difficult to acquire government funding for his work. Indeed, he would have found that research into the workings of the universe does not qualify as one of the “strategic research areas” identified by our national funding body, Science Foundation Ireland. I suspect the letter will provoke an angry from certain quarters, but it is tragically true.

Update

The above notwithstanding, it’s important not to overstate the importance of one scientist. Indeed, today’s Sunday Times contains a good example of the dangers of science history being written by journalists. Discussing Stephen’s 1974 work on black holes, Bryan Appleyard states  “The paper in effect launched the next four decades of cutting edge physics. Odd flowers with odd names bloomed in the garden of cosmic speculation – branes, worldsheets , supersymmetry …. and, strangest of all, the colossal tree of string theory”.

What? String theory, supersymmetry and brane theory are all modern theories of particle physics (the study of the world of the very small). While these theories were used to some extent by Stephen in his research in cosmology (the study of the very large), it is ludicrous to suggest that they were launched by his work.

 

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Snowbound academics are better academics

Like most people in Ireland, I am working at home today. We got quite a dump of snow in the last two days, and there is no question of going anywhere until the roads clear. Worse, our college closed quite abruptly and I was caught on the hop – there are a lot of things (flash drives, books and papers) sitting smugly in my office that I need for my usual research.

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The college on Monday evening

That said, I must admit I’m finding it all quite refreshing. For the first time in years, I have time to read interesting things in my daily email; all those postings from academic listings that I never seem to get time to read normally. I’m enjoying it so much, I wonder how much stuff I miss the rest of the time.

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The view from my window as I write this

This morning, I thoroughly enjoyed a paper by Nicholas Campion on the representation of astronomy and cosmology in the works of William Shakespeare. I’ve often wondered about this as Shakespeare lived long enough to know of Galileo’s ground-breaking astronomical observations. However, anyone expecting coded references to new ideas about the universe in Shakespeare’s sonnets and plays will be disappointed; apparently he mainly sticks to classical ideas, with a few vague references to the changing order.

I’m also reading about early attempts to measure the parallax of light from a comet, especially by the great Danish astronomer Tycho de Brahe. This paper comes courtesy of the History of Astronomy Discussion Group listings, a really useful resource for anyone interested in the history of astronomy.

While I’m reading all this, I’m also trying to keep abreast of a thoroughly modern debate taking place worldwide, concerning the veracity of an exciting new result in cosmology on the formation of the first stars. It seems a group studying the cosmic microwave background think they have found evidence of a signal representing the absorption of radiation from the first stars. This is exciting enough if correct, but the dramatic part is that the signal is much larger than expected, and one explanation is that this effect may be due to the presence of Dark Matter.

If true, the result would be a major step in our understanding of the formation of stars,  plus a major step in the demonstration of the existence of Dark Matter. However, it’s early days – there are many possible sources of a spurious signal and signals that are larger than expected have a poor history in modern physics! There is a nice article on this in The Guardian, and you can see some of the debate on Peter Coles’s blog In the Dark.  Right or wrong, it’s a good example of how scientific discovery works – if the team can show they have taken all possible spurious results into account, and if other groups find the same result, skepticism will soon be converted into excited acceptance.

All in all, a great day so far. My only concern is that this is the way academia should be – with our day-to-day commitments in teaching and research, it’s easy to forget there is a larger academic world out there.

Update

Of course, the best part is the walk into the village when it finally stops chucking down. can’t believe my local pub is open!

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Dunmore East in the snow today

 

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Revolutions in Science at UCD

Earlier today , I gave my first my undergraduate lecture at University College Dublin (UCD). The lecture marked the start of a module called Revolutions in Science, a new course that is being offered to UCD students across the disciplines of science, engineering business, law and the humanities.

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As far as I know, this is the first course in the history and philosophy of science (HPS) offered at an Irish university and I’m delighted to be part of the initiative. I’ve named my component of the module Science, Society and the Universe – a description of the evolution of ideas about the universe, from the Babylonians to the ancient Greeks, from Ptolemy to Copernicus, from Newton to Einstein (it’s a version of a module I’ve taught at Waterford Institute of Technology for some years).

Hopefully, the new module will be the start of a new trend. It has long surprised me that interdisciplinary courses like this are not a staple of the university experience in Ireland. Certainly, renowned universities like Harvard, Oxford and Cambridge all have strong HPS departments with associated undergraduate modules offered to students across all disciplines. After all, such courses offer a very nice mix of history, philosophy and science, not to mention a useful glimpse into the history of ideas.

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In the meantime, I think I will really enjoy being back at my alma mater once a week. I can’t believe how UCD has developed into a really attractive campus

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Summer hols; summer school, swimming and that book

You must be finished for the summer? Like most academics, I get asked this question every day in summer, usually by village acquaintances convinced that college closes the day the students finish their exams.

Some lecturers in the Institutes of Technology do indeed take off from June 20th to September 1st; that is their right, given the heavy teaching load during termtime. However, for those of us who try to keep up the research, the summer months are the time to get something done, just like our colleagues in the universities.

For me, this is no chore  – the sheer bliss of being able to do quiet research without classes, meetings, staff interactions and all the rest of it. Very restful. Also, we’re having a serious heatwave in Ireland this month and I’m happy to escape to the cool, quiet office every day. So I plug away happily during the day and treat myself to a swim in my village in the evenings..

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Tide’s in on Lawlor’s Strand in Dunmore East

Actually, I did give some ‘cameo’ lectures this week and last, to our summer school. We have a very nice bunch of engineering, computing and business students visiting from Kiel in Germany, and I had fun trying to condense my climate science course down to a one-hour presentation for each group. I haven’t given short presentations on climate before, it was very satisfying to prepare (see here for a copy of the talk)  The other thing I noticed was that students from the continent always seem to be very mature, polite and interested. I must look into an exchange sometime, do they have Erasmus for staff?

My main task this summer is to finish my little book on cosmology. It’s based on a course I have taught for some years and it’s been a lot of fun to write. Now I’m finding that it’s one thing to write a book and quite another to get it published! Still, I have plenty of time now to be writing book proposals and writing to publishers. In the meantime, I look forward to a swim in the sea everyday after work and a walk into the village. It’s funny to live in a village where others come for summer holidays!

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Tide’s out on Lawlor’s Strand in Dunmore East

Update

Unfortunately it’s so warm, we’re beginning to get quite a few jellyfish. Hope it cools down a little next week!

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A day in the life

There is a day-in-the life profile of me in today’s Irish Times, Ireland’s newspaper of record. I’m very pleased with it, I like the title  – Labs, lectures and luring young people into scence  – and the accompanying photo, it looks like I’m about to burst into song! This is a weekly series where an academic describes their working week, so I give a day-to-day description of the challenge of balancing teaching and research at my college Waterford Institute of Technology in Ireland.

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Is this person singing?

There is quite  a lot of discussion in Ireland at the moment concerning the role of  institutes of technology vs that of universities. I quite like the two-tier system – the institutes function like polytechnics and tend to be smaller and offer more practical programmes than the universities. However, WIT is something of an anomaly – because it  is the only third level college in a largeish city and surrounding area, it has been functioning rather like a university for many years (i.e. has a very broad range of programmes, quite high entry points and is reasonably research-active). The college is currently being considered for technological university status, but many commentators oppose the idea of an upgrade – there are fears of a domino effect amongst the other 12 institutes, giving Ireland far too many universities.

It’s hard to know the best solution but I’m not complaining – I like the broad teaching portfolio of the IoTs, and there is a lot to be said for a college where you do research if you want to, not because you have to!

Update

I had originally said that the institutes cater for a ‘slightly lower level of student’. Oops! This is simply not true in the case of WIT, given the entry points for many of the courses I teach, apologies Jamie and Susie. Again, I think the points are a reflection of the fact that WIT has been functioning rather like a university simply because of where it is.

Comments on the article are on the Irish Times page

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Resistors in series and parallel

In the last post, we saw that for many materials, the electric current I through a device is proportional to the voltage V applied to it, and inversely proportional its resistance, i.e. I = V/R (Ohm’s law). If there is more than one device (or resistor) in a circuit, the current through each also depends on how the resistors are connected, i.e., whether they are connected in series or in parallel.

In a series circuit (below), the resistors are connected one after the other (just as in a TV series, one watches one episode after another). The same current runs through each device since there is no alternative path or branch, i.e.  I = I1 = I2. From V = IR, we see the voltage across each device will be different; in fact, the largest voltage drop will be across the largest resistance (just as the largest energy drop occurs across the largest waterfall in a river). The total voltage in a series circuit is the sum of the individual voltages, i.e. V = V1+V2. As you might expect, the total resistance (or load) of the circuit is the simply the sum of the individual resistances, R = R1 + R2.

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Series circuit: the current is the same in each lamp while there may be a different voltage drop across each (V = V1+V2 +V3)

On the other hand, resistors in a circuit can be connected in parallel (see below). In this case, each device is connected directly to the terminals of the voltage source and therefore experiences the same voltage (V = V1=V2). Since I = V/R , there will be a different current through each device (unless they happen to be of equal resistance) .The total current in a parallel circuit is the sum of the individual currents, i.e. I = I1+I2. A strange aspect of parallel circuits is that the total resistance of the circuit is lowered as you add in more devices (1/R = 1/r1 + 1/r2). The physical reason is that you are increasing the number of alternate paths the current can take.

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Parallel circuit: the voltage is the same across each lamp but the currents may be different (I = I1+I2)

Confusing? The simple rule is that in a series circuit, the current is everywhere the same because there are no branches. On the other hand, devices connected in parallel see an identical voltage. In everyday circuits, electrical devices such as kettles, TVs and computers are connected in parallel to each other because it is safer if each device sees the same voltage source; it also turns out to be more efficient from the point of view of power consumption (an AC voltage is used, more on this later).

In the lab, circuits often contain some devices connected in series, others in parallel. In order to calculate the current through a given device, redraw the circuit with any resistors in parallel replaced with the equivalent resistance in series, and analyse the resulting series circuit.

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Problem

Assuming a resistance of 100 Ohms for each of the resistors in the combination circuit above, calculate the total resistance of the circuit. If a DC voltage of 12 V is applied, calculate the current in the circuit. (Ans: 133 Ω, 0.09 A)

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Current, voltage and the French resistance

Last week, our 1st science students had their first laboratory session on electrical circuits. They haven’t met electricity in lectures yet, so I spent some time explaining the concepts of current and voltage.

In essence, current is the flow of electric charge around a circuit (measured in amps) while voltage is the energy that drives the current (and is measured in volts). I find it helpful to think of the two in terms of cause and effect; a current will only flow in the circuit if a voltage is applied. In simple circuits, this energy is supplied in the form of a DC battery (or voltage source) that drives the current through some device (or resistor) in the circuit.

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The lamp (or resistor) lights as the current goes through it, completing the circuit

You might expect that there is a simple relation between voltage and current, and sure enough, the German scientist Georg Ohm discovered that, for many materials, there is a linear relationship between the two. Ohm’s law states that the current I passing through a material connected to a voltage V is given by the simple equation I = V/R. Here, 1/R is the constant of proportionality and is called electrical resistance and you can see why from the equation: a material with a very large value of R will pass almost no current (bad conductor), while a material with very small R will yield a large current for the same voltage (good conductor). So the term has exactly the same meaning as it has in ordinary speech, e.g. the French resistance. Resistance is measured in volts per amp, also known as Ohms (Ω).

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Many materials have a linear relation between voltage and current – the slope of the graph is the material’s resistance

In the experiment, the students apply a series of voltages to an unknown resistance in a circuit, and record the corresponding currents. A plot of voltage versus current then allows them to verify the linearity of the relation and the resistance is estimated from the slope of the line. (Strictly speaking, one should really put the voltage on the x-axis as it is the independent variable, but the calculation is simpler if the voltage is on the y-axis).

Measuring current and voltage

All of the above is fine in principle. Yet novices find the measurements quite difficult in practice. They have problems connecting the circuit because they get confused between measuring the current that flows through a device, and the voltage across it. It’s crucial to understand the difference between the two, and I suspect the modern multimeter adds to the confusion.

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The ammeter reads the current running through the resistor while the voltmeter reads the voltage across it. A plot of voltage vs current gives a measurement of the resistance

When I was a student, the current was measured by passing the current through an ammeter (marked A in the diagram), an analog device with a nice big dial calibrated in amps or milliamps. The voltage across the resistor was measured by connecting a different instrument, the voltmeter, across the terminals of the resistor; this voltmeter was a separate meter with a dial calibrated in volts (marked V in the diagram). So an ammeter was always connected in series with the resistor/device, while the voltmeter was always connected across it (in parallel).

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Current is measured by passing it through the ammeter (L) while voltage is measured by connecting across the voltmeter (R)

Nowadays, identical instruments are used for both; to measure current, one passes the current through the terminals marked ‘current’ of a multimeter, and the main dial on the meter is switched to the amp scale. To measure voltage, one connects the ends of the resistor across the terminals marked ‘voltage’ on an identical multimeter, and the dial is switched to volts. It sounds simple, but it’s easy to connect to the wrong terminals, getting no readings or blowing the fuse in the meter. More subtly, I think the clever circuity inside the multimeter hides the fact that current goes through while voltage drops across. All in all, I suspect students would understand circuits better if  we went back to separate instruments for measuring current and voltage….

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The mysterious multimeter. To measure current, leads are connected to the sockets marked ‘common’ and ‘amps’; to measure voltage, one connects to the sockets marked ‘common’ and ‘voltage’.

Notes

1. If a 12-V voltage is applied across a resistor of 15, what current flows in the circuit? How many electrons per second does this current represent? (Ans: 0.8 mA,  5.0 x 1015 electrons)

2. What happens to the current if one end of the resistor accidentally touches the other? (Ans: the circuit resistance drops almost to zero and the current becomes very large – don’t try this in the lab!)

3. Ohm’s law is a misnomer – it is not a universal law of nature but simply a property of some materials (many materials have a nonlinear response to voltage, including your cat).

4. It might seem from Ohm’s law that a material with zero resistance can give infinite current! No such materials are known; the relation is simply not valid for these materials. However, some materials have extremely low resistance at very low temperatures, known as superconductors. A good application of superconductivity can be found at the Large Hadron Collider, where protons are guided around the ring by magnets made of superconducting material: this reduces power consumption enormously but the snag is that the entire accelerator has to be kept at extremely low temperatures during the experiments.

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