Preparing for a PhD Interview in Physics

Posted in Biographical, Education, The Universe and Stuff with tags , , , on February 1, 2016 by telescoper

The other day I was chatting to a group of our 4th-year MPhys students about the process for applying  (and hopefully being interviewed) for a PhD. This is the time when students in the UK have started to apply and are awaiting decisions on whether they have to go for an interview. Final decisions are usually made by the end of March so those with interviews have a busy couple of months coming up.

I actually quite enjoy doing PhD interviews, because that involves giving excellent young scientists their first step on the ladder towards a research career. I’m sure it’s not so pleasant for the candidates though. Nerves sometimes get the better of the students in these interviews, but experienced interviewers can calibrate for that. And if you’re nervous, it means that you care…

The question, in case you’re interested, was to estimate the angle through which light  is deflected by the Sun’s gravity. I hadn’t done any general relativity in my undergraduate degree, so just did it by dimensional analysis which is easy because an angle is dimensionless. That gets you within a factor of a two of the correct answer which, in those days, was pretty goood going for cosmology. That seemed to go down well and they offered me a place … which I turned down in favour of Sussex.

In those days, before detailed information about research in University departments was available online, the interview generally consisted of a discussion of the various projects available and a few odd questions about Physics (and possible Astronomy) to see if the candidate was able to think on their feet (i.e. without fainting).

Nowadays it’s a bit different. You can still expect a bit of questioning about undergraduate material but that is normally preceded by the chance to talk about your final-year project. One reason for that is that selectors are interested in project work because it can provide evidence of an aptitude for research. The other is simply that it gives the candidate a chance to get over any initial nerves by talking about something that they hopefully know well, as they will have been working on it for some time.

My first piece advice for students who have been offered an interview, therefore, is to prepare a short (~10 minute) verbal summary of your project work so you’re not wrong-footed if asked to talk about it.

Students nowadays are also expected to know a bit more about the thesis topic in advance, so my second tip is to  read up a bit of background so you can talk reasonably intelligently about the proposed research. If, for example, you have decided to work on Dark Energy (as many seem to these days), you won’t come across very well if you don’t know what the main issues are. What’s the observational evidence? What kind of theories are there? What are the open questions? Same goes for other fields. It also will do no harm if you read a couple of recent papers by your prospective supervisor, for reasons of flattery if nothing else.

Anyway, I think those are the two main things. If anyone has other advice to offer prospective PhD students, please feel free to add via the comments box.

A Question of Magnitude

Posted in Cute Problems, Education, The Universe and Stuff with tags , , , on January 30, 2016 by telescoper

A frequent complaint raised by students of Astronomy is that astronomers insist on using funny units. Chief among them is the use of magnitudes to quanitify the brightness of an object. Why not use the observed intensity (or brightness or flux) of the light from the star, which can be expressed straightforwardly in SI units, instead of faffing around with a clunky logarithmic measure? The reason we use the magnitude scale is primarily historical and based on the fact that the eye’s response to light is more-or-less logarithmic and that in the days before calculators it was easier to deal with very large and very small numbers using logarithms.Most relevant calculations involve divisions and multiplications which become subtractions and additions when you use logarithmic quantities.

It was Norman Pogson who first suggested that a magnitude scale be defined such that a difference of five magnitudes should correspond to a factor of 100 in actual brightess. This was because the brightest naked-eye stars – those of first magnitude – are about 100 times brighter than the faintest naked-eye stars, which are of sixth magnitude. That was in 1856 and we’ve been stuck with it ever since!

Although the magnitude system may appear strange, it’s not really that hard to use when you get used to it. A beginner really just needs to know a few key things:

1.  Bright things have lower magnitudes (e.g. first magnitude stars are brighter than second magnitude stars);
2.  If two stars have apparent magnitudes $m_1$ and $m_2$ respectively then $m_2-M_1=2.5\log_{10} (I_1/I_2)$ where $I_1$ and $I_2$ are respectively the fluxes received from the two stars;
3. The intensity of light falls off with the square of the distance from the source;
4.  The absolute magnitude is the apparent magnitude a star would have if it were 10 parsecs from the observer;
5. Most stars have roughly black-body spectra so their total intrinsic luminosity depends on the product of their surface area (i.e. on the square of the radius) and the fourth power of the surface temperature.

Got it?

To test your understanding you could try these little problems. To warm up you might look at I posted the first of them a while ago. Anyway, here we go:

1. A binary system at a distance of 100 pc has such a small separation between its component stars that it is unresolved by a telescope. If the apparent visual magnitude of the combined image of the system is 10.5, and one star is known to have an absolute visual magnitude of 9.0, what is the absolute visual magnitude of the other star?
2. Two stars are observed to have the same surface temperature, but their apparent visual magnitudes differ by 5. If the fainter star is known to be twice as far away as the brighter one, what is the ratio of the radii of the two stars?
3. A binary system consists of a red giant star and a main-sequence star of the same intrinsic luminosity. The red giant has a radius 50 times that of the main-sequence star. (i) If the main-sequence star has a surface temperature of 10,000 K, what is the surface tempature of the red giant star? (ii) If the two stars can’t be resolved the combined system has an apparent magnitude of 12, what are the apparent magnitudes the two component stars would have if they could be observed separately?

Answers through the comments box please! The first correct entry wins a year’s free subscription to the Open Journal of Astrophysics…

Physics & Astronomy at Sussex – The Videos!

Posted in Brighton, Education with tags , , on January 20, 2016 by telescoper

So the annual University admissions cycle is getting into gear, which means I’ll be spending quite a few Saturdays giving talks and chatting to prospective students and their parents. As we prepare for  the first of Applicant Visit Days at the University of Sussex (on Saturday 23rd January) we’ve produced a number of videos featuring current students in the Department of Physics & Astronomy. I thought I’d share a couple here.

First here’s Anjelah, a student on our 4-year MPhys degree in Theoretical Physics. She still seems quite keen, despite having taken my Theoretical Physics module in her second year!

Here’s Joe, a 4-year MPhys (Physics) student:

And here’s another by Linn, who is on the BSc in Physics with Astrophysics degree:

You’ll notice that both of them talk about our dedicated study spaces, which the students really like. We’re one of the few Physics & Astronomy Departments in the UK – in fact the only that I know of – that has turned over the management of a large suite of rooms over to our students. We don’t just allow them to use the rooms 24 hours a day; we also give them a budget for furniture and books and they basically decide what they want and how to arrange it all. We also provide a constant supply of free tea and coffee (although I have to admit that I do pop in there from time to time and help myself too).

The Renaissance of Sussex Physics

Posted in Education, The Universe and Stuff with tags , , on January 10, 2016 by telescoper

I’m grateful to Darren Baskill for compiling this plot which shows the number of graduates in Physics (including Astrophysics) from the Department of Physics & Astronomy at the University of Sussex since 2004.

The last two columns are projections, of course, but we can be rather confident about the numbers. The increase over the last few years is predominantly a result of having  more students enter our Physics programmes, but there has also been a significant increase in progression  rates (as a consequence of excellent teaching), which is why we think the predicted numbers of graduates in 2016 and 2017 are likely to be accurate.

One reason for the recent growth was that in 2008 – a particularly low year on the above graph – the Higher Education Funding Council for England (HEFCE) recognized that Physics departments in the South East were struggling to recruit sufficient numbers of students to be financially viable. This led to the formation of SEPNet, a five-year programme which resulted in an injection of cash to promote physics across the South East of England via a range of activities, including a vigorous outreach programme. This almost immediately began to increase the number of applications to do Physics at Sussex (and indeed across the SEPNet consortium), with the result that 3-4 years later the number of graduates started to climb. SEPNet-2, which started in 2013, has developed this initiative still further, with new initiatives in collaborative graduate education.

(For the record note that I took over as Head of School at the beginning of 2013. I will make no further comment…)

This increase in student numbers has generated more income for the Department, all of which is invested back into teaching, research and other activities (including more outreach!) to create a broader curriculum, more choice for students, and more teaching staff;  the number of staff in Physics & Astronomy has increased from 23 to 40 since 2013, for example.

The income generated by this expansion has allowed us to broaden our research base too. This seems an appropriate time to mention that a new research group in Materials Physics has just been established within the Department. Professor Alan Dalton from the University of Surrey will be joining the Department next month as Professor of Materials Physics, and several further appointments will follow to establish a new research activity in his area of interest.

Alan’s research interests focus on understanding the fundamental structure-property relationships in materials containing one- and two- dimensional structures such as carbon nanotubes, graphene and other layered nanomaterials. Alan is  particularly interested in developing viable applications for nano-structured organic composites (mechanical, electrical and thermal). He is also interested in the directed-assembly and self-assembly of nanostructures into functional macrostructures and more recently interfacing biological materials with synthetic inorganic and organic materials and associated applications.

I’m delighted by this development, which will not only create an entirely new research activity but also add significantly to the range of options we can offer students, as well as new opportunities for undergraduate projects and placements. It also has enormous potential to build links with other Departments, especially Chemistry (which is part of the School of Life Sciences).

To end with, I thought I would also comment on another chart that Darren produced:

Apart from showing the very high levels of achievement of our students, this provides quantitative evidence of something I had suspected for some time. Although the proportion of female Physics students overall has hovered around 23% with little change since 2004, the propotion of female students getting first class degrees is significantly higher than for male students.

So there you are. Women are better at Physics than men. Discuss.

The Higher Education Green Paper – Expert Commentary

Posted in Education with tags , , , , on November 6, 2015 by telescoper

Hot news in Higher Education today is that the long-awaited Higher Education Green Paper is now published. A summary of this discussion document which is called Fulfilling our Potential: Teaching Excellence, Social Mobility and Student Choice can be found here. I haven’t got time to provide a detailed response this morning, so I will defer to an acknowledged expert on the subject of “fulfilling potential”, Dylan Moran:

From Physics to Powerlifting!

Posted in Education, Sport on November 3, 2015 by telescoper

I couldn’t resist posting a quick item relating to Nathaniel Wiesendanger Shaw, a student in the Department of Physics & Astronomy here at the University of Sussex. Nathaniel is a student on our Theoretical Physics (Research Placement) programme, which means that he works during the summer gaps in his course attached to one of our research groups. He also survived my attempts to teach the joys of Green’s functions, conformal transformations and assorted topics in mathematical physics when he was in his 2nd year.

However that’s not the focus of a recent news item about him. Here he is in action:

In fact Nathaniel is an accomplished powerlifter and, after a win in the All England Powerlifting Championships in August, he will soon be travelling to Canada to compete in the Commonwealth Championships in Vancouver. I don’t know the first thing about powerlifting, but I think this story just demonstrates that physics students can and do get involved in interesting stuff outside physics. In fact when I welcome new students at the start of each academic I stress how important it is to achieve a balance between work and life. I honestly believe that taking a break from studies to do something different every now and then – whether it’s sport or music or whatever – actually makes you a better student.

Anyway, good luck to Nathaniel in Vancouver in December!

Helping Blind Students with Mathematics and Physics

Posted in Education with tags , , , , on October 16, 2015 by telescoper

This short video clip features Daniel Hajas, a third-year theoretical physics student in the Department of Physics & Astronomy at the University of Sussex who has been working on technology intended to help visually impaired students to   engage with the charts, graphs and equations involved in studying mathematics and physics. Here is a news item arising from a recent poster competition for which Daniel, who is himself visually impaired, highlighted the challenges faced by blind students by exhibiting a completely blank poster, explaining that this was how a blind person would experience a complex equation. In the video he explains a little more about the work he has been doing.