Tag Archives: Physics

Testing the Wave Equation in a Gratnells Tray

Ripple tank experiments are not really class practicals, they are usually demos, but we do a block of work on Waves in Y8 and again in Y10 and so I wanted some practical work to go with it. The fact that the GCSE has a required waves practical that is really only a demo added impetus to my thinking.

I started with the classic AQA A level ISA experiment (PHY-3T-Q09) where multiple crossings of a gratnells tray are timed and the waves’ speed is calculated, and tried to build something from there.

By adding clockwork dippers made from chattering teeth toys to make a wave train, we got a set of practicals that work quite well. However, the match between the measured wave speed and calculated wave speed from the wave equation is far from perfect. I think there are probably two reasons; the dipper frequency varies quite a lot (we could extend things by getting students to measure their own dipper frequency instead of demoing the measurement of one, as has been our practice so far), and I have a suspicion that the single waves do actually run a bit faster than the wave trains made by the dipper.

The worksheets (follow the link below) are for four or five lessons and are deliberately tough. We leave higher groups pretty much to their own devices with them and give more help to lower groups. We’ve tried it with several groups now and think it has some value.

Waves Practicals

I’ve left in the notes for the two speed of sound experiments, which we only do, a bit later on in the course, if we have time.

If more of us take this up then I am hoping someone will have a good idea for making a more reliable dipper, or even get someone to manufacture one.

Notes for Y8 Energy

These are currently (August 2017) incomplete because I need to add in some HW exercises.

The Waves portion for Y8 is my next job.

Energy purists will notice that I haven’t adopted the energy newspeak. This because we use CIE for our GCSE; CIE have not yet indicated that they will go over to newspeak. I think (having looked at their sample exams) that someone who used this approach would be OK in taking the new AQA GCSE, which is deliberate because some of our boys change schools and because CIE might change eventually.

Y8 Physics Course Notes Energy

Energy – Names, Stores, and All That

Energy

If you’ve found this blog then you probably know that the way Energy is taught has been under discussion, and that the wording required by the Physics GCSEs has been changed for first teach 2016.

If you want help with this change then your starting point should be the IoP because as far as I can tell this new wording is their baby, and they do provide plenty of online as well as face to face support:

http://www.practicalphysics.org/energy.html

http://supportingphysicsteaching.net/En02PN.html

There are also teachers starting to blog their ideas about how to convey the change to your students, one that caught my attention recently was by Neil Atkin:

Teaching Energy – The ‘New’ Approach with Stores and Pathways

I’d also suggest that you sign up to http://www.talkphysics.org/ because there are plenty of people on there who will help.

The aim of this blog is, however, not to help, but rather to question the whole point of the change. I know that from a regulatory point of view it is a battle that has been lost, at least at GCSE level, but that doesn’t mean that we all have to line up and cheer.

So why do I object, is it just because I’m a curmudgeon for whom change is difficult? Well true as that might be, I hope it isn’t the only reason. I’ll start with one concern, and I can expand out to others if anyone is interested.

Before I start I guess I should nail my colours to the mast. I think that the idea that kids construct mental models of the world (Piaget) which they add to, or (very rarely) replace, in response to science lessons has a lot of value in explaining kids’ understanding of science.

Prior to first reading about the changes on TalkPhysics I hadn’t really given the way we teach energy much thought; we introduce the names in Year 8 and use them to frame the ideas that Energy is a Physics topic with Physics language that differs from everyday language and that Energy must be conserved. We do some questions with regard to efficiency, talk about perpetual motion machines, do one efficiency experiment and that’s it, we don’t think about it again until we can start to quantify Energy at the end of Year Nine, start of Year Ten. OK so we lament the rather silly questions where they have to write out the transformations. At best those questions are trivial, at worst they encourage the kids to think that the amount of energy dissipated via sound is as significant as that via heat.

Having named the types we go on to Thermal Physics, and it is here that we have to engage in a fight to break their preconceived models – in particular that Thermal Energy is a thing. We all know the “Explain Convection” “Heat Rises, Sir”  problem. If you were able to ask any nineteenth century Physicist I’m sure they’d tell you just how seductive the “Caloric” heat as a fluid model is. I suspect that naïve versions of Caloric are just the models which many of today’s kids construct for themselves, try as we might to oppose it.

I actually think that the names help with this. If heat is Thermal Energy, but Thermal Energy can just as easily be Kinetic Energy or Electrical Energy, then a mental model of heat as a fluid becomes just that little less tenable.

It is here, I think, that the differences between my impression of kids’ thinking and the “Stores and Pathways” (hereafter S&P) advocates’ impressions begin to strongly diverge. One of the arguments made against the names approach (hereafter Names) is that it leads to the kids believing that each of the named energies is a different physical thing. I’m not convinced that ours give it that much thought, and isn’t that something that can be minimised through the teacher’s emphasis? Of course, if the S&P advocates are right then Names hasn’t helped because if Thermal Energy is a separate thing then it can have a separate physical manifestation (i.e. be a fluid) from the other energies in a mental model of the world. But if their model is to be consistent doesn’t it require a whole set of pathways creating to explain how one physical manifestation of an energy type transforms itself into another?

If you have seen those pictures of vats of yellow fluid that accompany this topic then you have probably seen where I am going with this.

Energy is abstract. The S&P advocates continually emphasise the idea, which they give Feynman’s authority to, that it is just an accounting tool. Kids don’t like abstract ideas, you don’t have to be a died in the wool Piagetian to know that they shy away from them. What is the IoP sanctioned response to this when teaching abstract ideas like Energy or Electricity? Offer an analogous model. Anyone who has ever been to IoP training has probably passed a rope loop hand to hand to represent electrons in a circuit. And what is the model in this case? Vats of yellow liquid.

So the S&P advocates oppose Names in part because it gives a reality to the “accounting tool” that is energy, and then back this up with pictures of energy as a yellow liquid.  How can they not see that they are reinforcing the very problems that everyone already has – getting away from the fluid model of heat and getting away from the idea that energy is a thing? They even provide pathways from one vat to another so if you were worried that your yellow fluid has to have different properties when it is Thermal rather than say Kinetic you have a mechanism for change.

And don’t get me started on the thought that those pictures surely have to give the kids – that there will come a point when the stores are filled – and what happens then? When I asked this on TalkPhysics the implication was that I was a bit dim for not realising that the tanks drawn in the pictures were not real, well possibly, but I’m not 13 with a dislike of Physics.

 

 

 

 

 

AS Physics – Particles

Both my old (Beithaupt) and my new textbook (England etc) for AQA AS Physics seem to like to do particles in the opposite order from tradition. The trouble with this is you are talking about photons before you’ve explained where the idea comes from. I’m afraid I’m traditional and like to teach it from a historical point of view. To that end I follow this timeline:

Particles Early Timeline

When I get towards the photoelectric effect I follow the history as laid out by Klassen:

Klassen_on_the_Photoelectric_Effect

I illustrate the history with an apparatus diagram from Von Lenard’s Nobel Lecture:

Lenard

And the graph that Millikan produced when trying to disprove it, from his Nobel Lecture:

millikan_nobel-lecture

And although not strictly in the A level, having introduced De Broglie, I like to go through the Bohr atom as well:

Hydrogen and Bohr

 

 

Pendulums Project

This is a project that we give to Year Nine across six hour long lessons – which in our case takes six weeks. It was inspired by reading about the dutch method of teaching science as recorded in the TIMSS International Video study. The Dutch seem to set assignments that require the students to pace themselves through long term assignments, and as our school was having a push on independent learning I thought I’d dip a toe in the water.

The project is mostly about experimental design and utilises the fact that we have enough datalogging kit for classes to be able to measure the period of a pendulum in more ways than just hand timing.

We’ve been doing this project for at least four years now. The boys don’t like it much – especially the top sets, because we refuse to help them and they are used to being able to get our help in setting experiments up, but I, and I hope my department, think it is a useful exercise. It certainly means that we do not have to bother covering pendulums again until Y13!

Pendulums(1)

They are always surprised when they get an increase in time with swing size (pendulums only do SHM for angles of roughly 6 degrees or less) – our fault for the way we introduce pendulums in Y7 I suspect. They often get a tend when changing the bob mass because they do not take into account the fact that the change moves the centre of mass. They do not know what to do when there is no trend – again our fault, we always set experiments that have trends. And they always conclude that the computer readings were better, when actually the resulting trend from that experiment is a curve and not a straight line because of the mass of rod and probably the inertia of the pulley. Even when they notice that it gives a curve, they still conclude that that was the better experiment!

I’m always thinking that I ought to do another, but although I do have a sixth form project along similar lines, I’ve never yet thought of a topic which inspired me to do another for KS3 or 4.

 

Writing Up a Practical

I suspect this will be the most contentious piece I’ll write, but I’ll hide it in “Resources” and it’ll never be found!

I have particular views about write-ups, and I tend to be pretty uncompromising about them, on the perhaps tenuous basis that many years ago I have had a couple of papers published on experimental Physics.

In KS3 and Ks4 the idea of an “investigation” is rather silly – the kids do not know enough about Physics, or even the kit that a department possesses, to design and test anything but the most trivial hypotheses with uninteresting experiments. Why then are we routinely expecting them to include “hypothesis” and “evaluation” in their lab reports – especially if it is an experiment we gave them instructions for in the first place? I know you can answer “because the ISAs require it”, but they’re gone now – and really?  Once again the hypotheses are so trivial there is just no need to have been reinforcing the process through the previous however many years. You are teaching them that science is trivial. As for “evaluations”, what can they evaluate? You are encouraging them to write “I enjoyed it and I think we did it well”. Who cares!!??

And so these are our write up instructions that must be followed throughout KS3 & 4 if they want a decent effort grade :

Writing_up_a_Practical

and the glossary:

Experimental_Glossary

For the level our boys work at, and certainly with a parent’s help, I regard the “Method” portion as pretty self explanatory, and so requiring these instructions to be followed frees up our marking effort of comments and advise for direction at what I regard as the hard bits – drawing and interpreting the graphs.

Just as an aside:

In a recent inspection of the department it was suggested that our exercise books were a confused mix of write ups, notes and problems. I’m trialing these lab books from Rhino for all write ups with a Y10 group to see whether this helps. So far it is going very well and I suspect that next year we will be rolling lab books out across more of the department.

KS3 Grading/Marking Policy

From what I read about marking in UK schools suspect that this is of very little use to anyone else, we aren’t ofsteded so I’ve no idea what they’d think.

Our school sends home regular updates with a level (yes we still do levels) and an effort grade from 1(good) to 5(so poor it is very rarely given). Parents are often less concerned by the level than by the effort grade, and so we have to be prepared to justify it to them and to the SLT. With this, and the idea that kids only read their grade and not the comments, in mind (boys don’t tend to be competitive about the amount of work they put in!), we stole an idea from our Maths Department, which has since spread to other departments. The idea is that homeworks should only be graded on their effort (ie 1 to 5) and that it should be the ticks and crosses and comments that convey how the Physics went. It is a lot easier to judge effort than level on single piece of work. Then a mean of the grades received since the last report home can be the easily justified effort grade on the next report home. It also means that boys in lower ability groups do not have to consistently get low grades. It has worked remarkably well, marking is much easier and when, as is quite often the case, our grades that are sent home are questioned as harsh we have our justifications ready.

Of course if you are going to go in this direction you have to make sure that you have documentation explaining your expectations in place, and so the following document is on our VLE, for the boys, but mostly for the parents:

A_Guide_to_Physics_Department_Effort_Grades

Imaging in Year 9

In Year Nine we have put several bits and pieces from across the KS3 and KS4 syllabus together into a topic that we called “Imaging”.

Imaging contains the obvious stuff like Pinhole Cameras, Lenses, the Eye, and the EM Spectrum, but also some less obvious stuff like False Colour Imaging.  False Colour Imaging is included because we have done quite a lot of work with the Faulkes Telescope Project where we obtain individual black and white images that need combining to give an RGB picture (there are some examples of our work on this site).

As with our Year 7 programme, textbook support for this work is a bit sketchy so we wrote some notes to support it:

Year 9 Imaging

And a worksheet for a lesson on False Colour Imaging based on Adobe Photoshop:

Using_Photoshop_to_put_together_False_Colour_Images

 

Year Seven Physics Textbook

Because we teach Physics as a separate subject from Y7 it is tough to find appropriate textbooks at KS3.

In Y8 we use a mixture of Johnson’s “Physics for You” and Philpott and Clifford’s “Physics 11-14”.

In Y9 we use “Physics for You”.

We’ve toyed with the idea of using Reynolds’s “Complete Cambridge Secondary 1”, but at the moment I can’t justify the cost.

All of which leaves us without a textbook for Y7 so we wrote our own as a PDF that the boys are then required to access through our VLE. Feel free to have a look and tell me what you think. (I’m not sure that every single exercise is our original work, so if you happen know where one came from, do let me know so that I can credit it – or remove it if it’s yours and you want me to!)

Y7 Physics