A graphic for respiration and human biology

resp in humansI made this a few years ago when I had a Y8 group, and I wanted to try and help them connect the Y8 digestion topic to the Y8 respiration/lungs topic we’d done previously.

Thank you to my colleagues at my previous school for their input/advice with this, especially about the difference between excretion and egestion (humans essentially being a donut, topologically speaking from a digestion point of view!).

Its a shame there’s not space for a zoomed in picture of villi, alveoli and blood vessels too.

Needless to say.,. *physicist doing biology warning!* Happy to receive feedback about wording, etc.

The ppt file can be downloaded here.

The lens equation

Just a quick post about the lens equation and its two formulations (and associated conventions):

(1) the ‘Real is Positive’ (RiP) formulation (and conventions):
1/u + 1/v = 1/f

(2) the ‘Cartesian’ formulation (and conventions):
1/u + 1/f = 1/v

Some of the differences between the two conventions are discussed nicely here, I won’t bother repeating that information (so maybe read that first if you’re not already familiar with this). But I do want to add a few comments; I couldn’t find what I wanted to say discussed elsewhere (but I didn’t look that hard…).

It is interesting that different UK exam boards specify different conventions to be taught:

  • Edexcel: RiP
  • AQA (in the optional medical physics topic): RiP
  • (OCR A – not included in the specification)
  • OCR B: Cartesian

This is what has brought this little curricular quirk to my attention…  I taught Edexcel at my previous school, but my new school does OCR B, so I need to adjust!

Here is what I would want to add to the IOP webpage:

The key difference between the two conventions is what positive and negative values of u and v represent. In the RiP convention, u is always positive, and the sign of v indicates whether a real or virtual image is produced. In the Cartesian convention, the signs of u and v indicate something different: they indicate which side of the lens the object and image are located on, with the optical centre of the lens being placed at the origin of Cartesian axes (there is a diagram here which illustrates this nicely).

This means that the RiP convention is set up so results of calculations contain information about the nature of the image (is it real or virtual), but no information about which side of the lens image forms (the ‘other’ side of the lens to the object, or the ‘same’ side of the lens as the object).

The Cartesian convention is set up to do the opposite: results of calculations contain information about which side of the lens image forms (the ‘other’ side of the lens to the object, or the ‘same’ side of the lens as the object) but no information about the nature of the image (is it real or virtual). 

Here is an illustration of this – it is the same question answered using both conventions. The question was: An object is placed 4cm from a convex lens which has a 12cm focal length. Calculate how far from the lens an image forms, and state what else the result of your calculation tells you about the image.

lenses

There is, therefore, different information which is ‘contained’ within the physics of the lens equation, in the two different formulations. And therefore, different information which then has to be ‘bolted on’ to the result of the calculation to complete the physics, for each formulation.

This is no problem to teach, though. Ignoring the case when u = f (no image forms, or an image forms at infinity), there are just three situations students need to learn, which I have set out below and colour-coded too, to illustrate the above. I would advocate students committing this information to their long term memories whichever formulation is taught. Here are the three situations:

(1) convex lenses produce real images ‘the other side’ of the lens to the object, when u > f

(2) convex lenses produce virtual images the ‘same’ side of the lens as the object, when u < f

(3) concave lenses produce virtual images the ‘same’ side of the lens as the object.

If the RiP convention is taught, the purple information is contained within the results/conventions of the calculation, but the blue information is not, Whereas, in the Cartesian convention, the blue information is contained within the results/conventions of the calculation but the purple information is not.

As I said before, learning the three situations in full will help students, whichever formulation is taught. But the best way to learn these will be explicit instruction followed by guided practice, with questions which ensure students reflect on (and summarise) both the nature and the location of each image produced. In my experience, if this is clearly modelled to students before they attempt it, they pick it up quite quickly. I have found the use of a visualiser extremely effective for this, and I know many others agree.

Here’s a link to my ray diagrams practice worksheet (originally a MS Publisher file). I firstly use this to teach students how to draw ray diagrams for lenses, this comes up at GCSE and A-level. But in the next A-level lesson, we can then use the lens equation to predict where the image should have been for each diagram and thereby check the diagrams drawn previously. It’s so rewarding when the maths from one lesson matches up perfectly to the diagrams drawn previously!

(I would add that I am in two minds about the images I have used for the objects on this worksheet… in exams the object is usually just a boring arrow. I think I would add a few boring arrow questions to the worksheet in future so students have practised these too. The images used could be argued to be distracting/adding an unnecessary complication (which part of the giraffe shall I draw the rays from? rather than just going from the top of an arrow every time)… but they do add a bit more variety and quirkiness to the practice. A few of my colleagues have successfully adapted/personalised Q8 too!)

 

A curriculum map of school science

As an exercise (translation: for fun?!), I attempted to make a map of ALL the different areas of school science / the school science curriculum, on a single powerpoint slide. Is it a “knowledge organiser”? Yes, it probably is – but for a whole subject (kind of), not just one topic. You can download it from here if you like. Feel free to use it, adapt it… or, even better… try doing your own from scratch and share what you come up with!

The first thing to say is that it is pretty rough and ready. I am not a designer and I am sure this could be re-formatted to look a lot nicer (without losing the important aspects of the arrangement/what has been placed next to what). If anyone would like to do this, please just go ahead and re-share!

ks3 map

By a ‘map’, I don’t mean one of those ‘road maps’ that were all over twitter earlier this school year, which simply show the (usually linear) order of study of different science topics at a particular school. That kind of curriculum map simply answers the question ‘what point am I at in the order of topics chosen at my school’.

I wanted to create a different kind of map, something which might help answer more general and more conceptual questions, such as:

  • What is school science about, what things do you study in school science, what is the scope of school science? What are the key objects and concepts?
  • How do the different areas connect and conceptually link with each other?
  • Where are we within science right now i.e. in this current lesson or topic? Not ‘where are we in the sequence of topics’ but where are we within science? In other words, where does this topic ‘sit’ within science as a whole? One intention with this map was to give myself something to point to at the start (or middle, or end) of a topic.

These are quite high-level questions. But I do think part of a science teacher’s job is to try and ensure students develop this kind of holistic picture of the different areas of science and how the ideas link and underpin each other. Rather than ending up seeing science as a procession through unconnected topics (cells, magnets, acids… etc). Science is a logical, interconnected web of knowledge, each part of science is connected to every other part of science, either closely (as with cells and evolution) or more distantly through shared foundations or differences in scale (as with evolution and forces… actually even this link isn’t that convoluted: evolution occurs through molecular processes within cells, but molecules interact with each other by means of forces. No Hollywood actor is said to be more than 6 steps from Kevin Bacon. Well, I would suggest that no scientific concept is more than 6 logical steps from any other scientific concept.).  There are very few (no?) contradictions or incommensurate parts within science.

 

phys

The same map with just Physics highlighted.

 

So, to help students gain this more holistic picture of science, can we not show them something to help them see? Why not try showing students what a map of science  might look like, with topics which clearly link to each other, closer together on the map.

This is quite ambitious. Science is a big subject (but aren’t they all) and there are so many possible links and arrangements that could be made summarising the curriculum.  I make no claim that my map is in any way definitive, it is the totally subjective attempt of one person, reflecting their particular knowledge and bugbears. There were subjective decisions to make about what to include and what to omit, what to put in bold, how much explanatory detail to include. I also decided to only map biology, chemistry and physics content knowledge. ‘Including areas such as ‘working scientifically’, knowledge of science as a discipline, mathematical and communication skills too would surely be impossible!

I’d love to see if anyone else has attempted anything like this. The differences in structure, arrangement and emphasis would be intriguing! I did make a token attempt at researching to see if anyone else has done this before – but I couldn’t find a single one. Lots of lovely mindmaps for individual topics or for individual sciences. But no maps of science as a whole… Please do contact me/share if you have something that attempts something similar across all three sciences, I’d love to see them.

 

bio

The same map with just Biology highlighted.

 

So… I wanted to show the different areas (topics) and objects of study in biology, chemistry and physics, all together side by side – so (possibly, in the future, maybe when I’m happier with the map and find the right class of students to show it to without overwhelming them) students can see the different foci of the three sciences more clearly. Many others And also to illustrate some of the links and the shared concepts, – something of the structure that we know is there. For example:

  • Energy goes across the top as a unifying concept and a useful tool for scientific analysis across all the sciences.
  • As the study of fundamental phenomena, Physics encircles/underpins chemistry and biology – although perhaps not completely (since although everything that happens, happens because of fundamental physics, it can be argued that categorically different processes and phenomena emerge at biological scales and complexity- e.g. evolution and ecosystems)
  • Chemistry forms a bridge between physics and biological phenomena
  • Chemical reactions and living things and cells are very closely linked, although photosynthesis and respiration are associated more with biology they are placed just as closely to chemical reactions
  • One significant place where the three sciences meet is in the study of Planet Earth – in space (physics), its origins (physics), its natural history (atmospheric chemistry, geology, biology), Earth’s material and energy resources (chemistry and physics), climate change (physical/chemical mechanisms), ecosystems/ environment/ pollution/ habitats/ interdependence/ environmental stewardship and sustainability (chemistry and biology)
  • Atomic structure – protons, neutrons and electrons, and the idea of charge – is a really important connection point between chemistry and physics – particularly for electricity as well as (obviously) for atomic and nuclear physics
  • I realised there are important curriculum links to be made across biology and chemistry/Earth science whenever fossils are discussed

I had hoped that making this ambitious cross-science map might illuminate future  curriculum planning … and I think some of the above points are relevant to that.

Why powerpoint? Not because I would necessarily want to project this, but mainly just because powerpoint is easier to work with when trying to produce a map with parts that I might want to move round in relation to each other. I’d probably be more likely to consider printing this ‘single slide’ on a single sheet, so students could study it more closely.

That said, I’m not sure whether what I’ve produced would be useful for many students yet. Its very text heavy; so it particularly might not be as suitable for learners with lower starting points or with lower literacy levels. Cognitive load would be very high.

 

chem

The same map with just Chemistry highlighted.

 

The map might make more sense/be more useful to students who already know a bit (or a lot) about the individual science topics, because their working memory won’t be overloaded processing all the details; their better prior knowledge will allow them to simply recognise the different areas, allowing them more capacity to pay more attention to the arrangement and the links. Its easier to learn about things we already know a lot about. Already knowing a lot about the different areas of science would significantly lower the cognitive load of studying this map, I imagine. Beware the ‘curse of the expert’ when reading it.

That said, I think you can sometimes learn a lot from studying an intricate map in detail – after all, who doesn’t love a novel that starts with a map to study on the inside cover?!

Once final point is that, sometimes, two concepts have been very deliberately placed closely together because they link. But other pairs of concepts might have ended up very close together but don’t have such an important link. That is a possible shortcoming of the current format/formatting. Very open to seeing if anyone can jiggle things around and improve this! Also, other pairs of concepts would ideally have been placed closer but I just couldn’t make it work (and there may have been other links to prioritise) e.g. Photosynthesis and light, particles and sound. I think I can get round this one though by preparing different versions of the map with relevant topics highlighted. E.g. at the start of a future lesson on photosynthesis I can return to the map but this time with photosynthesis, chemical reactions, molecules, the air, cells and light all highlighted – to flag to students that this lesson we will need to use prior knowledge from all those topics (perhaps prior to running a retrieval mini-quiz on those topics to activate that prior knowledge before the topic starts properly).

Knowledge relevant to Photosynthesis from across the sciences:

photosy

 

So… waffle over. Do have a look at the map (download the ppt version). I’m interested in having discussions about anything I have omitted, any wording you don’t like … even anything you might think is good! Maybe it might even be useful for thinking about future curriculum structuring or sequencing. Thanks for reading.

 

 

The map can also be used to show the domains(?) of  some other sciences, within science as a whole:

Biochemistry:
(I missed off electric charge and atomic structure here. Ions are important)

biochem

 

Medical and Health sciences – very much NOT “just biology”.
(again – I should have included electric charge and atomic structure)

health

 

Planetary, Climate and Environmental sciences:

Earth

 

Content that might be relevant to a Y7 cells topic (this might influence curriculum sequencing work):

y7cells

 

 

 

 

 

 

 

Remember: GCSE exam Qs DON’T have to be consistent, or fair

(disclaimer – yes, fine, this blog post title is a maybe bit sensationalist…)

It has taken me a LONG TIME to (partially) accept this. I’m still not sure I really agree. But I found an example today I wanted to share.

The primary purpose of final GCSE exam questions is not to fairly assess students’ knowledge of a course. It is to separate out students into grade bands, based on the knowledge specified in the course.

Look at this question from a 2018 GCSE Physics paper. This was question 10, right at the end of the paper, so was a high demand question designed to ‘stretch the top end’ and discriminate between students getting grades 7, 8 and 9. So, on average, students who get grades 4, 5 and 6 might be expected to score between 0 and 1 out of 4. Students getting grades 7 and 8 might score 1-3 marks and students getting grade 9s might get 3 or 4 out of 4. That is probably the purpose of this question.

From a 2018 GCSE Physics paper:

triple

Now, here (below) is a question from the following year, the 2019 GCSE Combined Science (CS) Physics paper, from the same exam board. This is a different question. It is question 4 on the Combined Science paper, so appears much earlier in the paper, and so is only a ‘standard/high’ demand question rather than the highest demand. This question is therefore doing a different job to the previous one. This question is aiming to discriminate between students who will get a 4/5 (who might be expected to get 1-2 out of 4, on average) and students who will get a 6 or 7 (who might be expected to get 3-4 out of 4, on average).

From a 2019 GCSE Combined Science Physics paper, same exam board:

combined

BIG REVEAL TIME!!!! (not). So – these questions look identical. The diagram is identical, they’ve even recycled the exact same diagram from the previous year. Very minor changes to wording mean it appears to be essentially the same question: Explain why current causes the coil to rotate. The only difference of any significance is that the triple paper has the word continuously at the end. But surely this shouldn’t affect the expected answers too much? Surely, these very-nearly-identical questions will have very-nearly-identical-if-not-identical markschemes?

markschemes

Things to note:

  • The first marking point in the GCSE Physics answer comes as the 3rd marking point in the CS paper (highlighted in blue). So they were expecting/wanting a different sequence.
  • “The current creates a magnetic field” was acceptable for the first marking point in GCSE physics, but was insufficient for the first marking point in CS the following year, when students had to have “the current creates a magnetic field and there is a magnetic field from the permanent magnet”
  • The idea of current being in opposite directions on either side of the coil (in yellow) was credited in the CS markscheme but apparently ignored in the GCSE Physics markscheme
  • The Physics markscheme credited a statement about the commutator swapping the connections to the coil every half turn (pink), but this was not creditworthy on the CS markscheme
  • Both questions credited the effect of the commutator swapping the connections every half turn, in terms of either (a) reversing the current every half-turn (green) or keeping (b) the direction of the current in or (c) the direction of the force on the ‘left’ and ‘right’ sides of the coil the same (red and purple). However the CS markscheme prioritises (b) and allows (a) and (c) whereas the GCSE Physics markscheme prioritises (a) and (c) but only allows (b)!
  • The GCSE Physics markscheme wanted mention of moments. Moments is a ‘triple only’ topic, so cannot be required on the CS markscheme.

This last point has an annoying implication: students studying GCSE Physics need to be taught a different explanation of electric motors (that refers to moments) than GCSE CS students. In my opinion, this revelation is feels unfair, since the specification content on electric motors is identical in both courses. When planning the lessons teaching students how to explain electric motors, how on Earth were teachers supposed to know this exam board would have different expectations for this explanation for each course?spec

 

Here are a couple of made-up example student answers.

The current in the coil creates a magnetic field. The magnetic fields interact to make the coil rotate. The split-ring commutator reverses the connections from the brushes to the coil every half turn. So the coil keeps spinning. 

I think this would score 0/4 according to the 2019 CS markscheme.
But it would score 3/4 according to the 2018 GCSE physics markscheme.

Here’s another one.

The coil is in a magnetic field and the current in the coil has its own magnetic field. The current in the coil flows in opposite directions on either side of the coil. So the forces act in opposite directions on either side of the coil and the coil spins. 

I think this would score 3/4 on the 2019 CS markscheme.
But only 1/4 on the Physics 2018 markscheme (the first mark – they probably don’t get the 2nd mark due to not mentioning the magnetic fields interacting to produce a pair of forces).

OK, these may be quite unusual answers. But I don’t think they are outside of the realms of possibility. Consistency? Fairness? What do you think?

 

In conclusion.

Firstly: despite these questions appearing to be virtually identical, they were marked very differently. Teachers who are teaching about electric motors at GCSE for this exam board cannot simply look back at a previous markscheme and say ‘OK – if this comes up and its worth 4 marks, this is what they want’. Based on this analysis, I have produced an explanation of electric motors which covers all/most of the marking points from these markschemes:

Explain how current causes a coil to spin (e.g. in an electric motor):

explanation.PNG

(one of these bullet points would be for GCSE Physics only, since it refers to moments).

Secondly – it looks like the word continuously in the triple question was more significant than I first assumed.

  • Explain why the coil rotates – mentioning the commutator is less important – only one mark related to the commutator.
  • Explain why the coil rotates continuously – need to include a more detailed explanation of the commutator (2 marks for this).

Thirdly – I find this kind of thing frustrating and annoying, as a classroom teacher trying to prepare students for exams. Specification statements like the above which require that Students should be able to explain X but give no indication of what different points that explanation will need to include. So we do our best, but its no surprise when students don’t do well on this question in the exam. For example, I might never have thought to teach students to explain motors by referring to moments. Moments are in a totally different topic. Another teacher may have thought about referring to moments in their electric motor teaching, but then decided against it since the electric motor content is identical in GCSE Physics and CS (see specification points above) so couldn’t refer to a triple-science only concept.

And fourthly – finally – there is the frustration that these almost identical questions had completely different markschemes in the space of 1 year, from the same exam board. The lack of consistency in the markschemes in the space of 1 year is startling.

But then – I remembered – exam questions don’t have to be fair, or consistent. They merely have to discriminate between candidates. And these two (almost identical) questions were actually performing very different roles in the two exams, as discussed at the start of this post. So why on Earth would we expect almost identical questions to have (almost) identical markschemes anyway?

This is the GCSE Science assessment regime we live in.

Booklet for GCSE Forces (part 1) (AQA)

Inspired by several blogs I’ve read this year about teaching through booklets (see below), I have made this. It only covers a small part of the AQA GCSE forces topic but this is an area riddled with misconceptions. So I hope it will be useful to people.

Please be kind with my writing… this is a first attempt and there is at least one page where I’m definitely not yet happy with the quality of the explanation I’ve written… I will try it out with a class at some point and adapt it (or ditch it completely) as I go. Do get in touch about any typos/errors/passages that accidentally reinforce misconceptions.

Anyone is welcome to use and adapt it. Hopefully it will save you planning time and help reduce workload and stop you needing to invent the wheel so much. The booklet pages/question sets can be easily converted into standalone worksheets if that’s how your lessons work (I’m currently trialling the ‘booklet’ style’ with my Y10s).

Please don’t put it on TES. If you do adapt/add to them and would like to re-share your versions please do so via twitter, @ me in (@physicsuk) and I’ll be happy to retweet.

If I have accidentally used any copyrighted images, please get in touch and I will take them down.

Acknowledgements/links for further reading

Obviously Ruth Walker has ‘written the book’ on this for physics (particularly here and here) and her GCSE Physics SLOP booklets were a starting point for mine. Our structuring of topics are similar, partly because I’ve looked at her booklets, but also partly because I think we’ve come to similar conclusions about the best ways to sequence ideas in this area of the physics curriculum. If any of my explanations have turned out similar its probably because I’ve read Ruth’s booklets, internalised them and now that’s how I explain it. Kudos.

Similarly – see Adam Boxer here for chemistry and @BioRachProject here for Biology.

This by Ben Newmark really influenced me – and also, more recently, this from an anonymous teacher on Adam Robbin’s blog. I think they’re both pretty persuasive. Hence my trial.

Ollie Lovell has also recently shared some GCSE Physics forces booklets so he gets a mention too! Scroll down his twitter feed to find them.

W=mg SLOP

Here‘s another GCSE Physics SLOP calculations worksheet – this time for W = mg.

I’ve been thinking really hard this year about how best to structure GCSE Physics calculation practice/SLOP. I’ve been influenced by other posts by @tchillimamp here and Adam Robbins here; this was my thinking a few months ago.

What has changed since then is that I have revisited AQA’s very helpful document, “Our Exams Explained“. If you teach AQA GCSE Physics or combined science you really, really should read this! Here’s the most helpful page for equations (p22) – it describes the types of calculation questions that will appear on the foundation papers (Low and Standard demand only) and the higher papers (Standard and High demand only).

eqns

So here is the perfect way of fading calculation SLOP worksheets for a specific equation. Start with low-demand questions (which give the equations in the question stem) and fade upwards towards the high demand questions.

I realised I’d been doing my lowest starting students a disservice by diving straight in with Standard Demand questions and not including practice of Low demand-style questions. I realised I’d never really taught my lowest starting students explicitly how to best set out these kind of questions where the equation is given to them. I’d been omitting opportunities to get them to practice what they will actually have to do in equation questions in the first 60% of the foundation tier exams (60% of FT is low demand questions). Memorising the equations can come later! With my new SLOP sheets I want to make this explicit for my lowest starting students.

Likewise, I’d been doing my highest starting students a disservice by not including enough high demand 4-6 mark (multi-step) calculations. I need to get better at embedding these throughout the course, as on the GCSE physics papers there’s usually at least two of these – that’s potentially 11-12 extra marks to gain. Similarly, I wasn’t always including practice questions requiring mathematical content like standard form, or volumes/areas calculations, ratios and percentages.

So, the mantra guiding all this is: what I want students to practice is what they’ll have to do in the exams. So, on my new style SLOP calculation worksheet…

– almost all questions should be ‘exam style’ i.e. a prose sentence where students have to pick out the data needed (no tables to fill in) – that’s what I want them to practice doing

– all questions should be followed by sufficient space for students to show their working fully, immediately after the question (no switching to separate sheets of paper). Equations lend themselves to vertical working (“line up all your equals signs”) down a page (rather than writing prose across a page) and the formatting encourages this

– questions which require W = mg are all mixed up with questions that require W/g=m and g = W/m. The process I want students to be practising is to (1) write the equation in letters (or words) in the form they’ve memorised (so W=mg for this one), (2) substitute, and THEN (3) change the subject if needed. I think a block of W/g = m questions followed by a block of W/m=g questions doesn’t get them to practice this process (rehearse this procedural knowledge?) as well.

 

I hope this is useful… and not too repetitive… I will share further SLOP worksheets in this style as I make them. If anyone reading this makes any in the same style please do email me (teachingphysicsuk@gmail.com) and I’ll add them to the same folder.

GCSE Physics F = BIL SLOP worksheet

Following @TChillimamp‘s post earlier this week I thought I’d also share my attempt at a SLOP worksheet for a GCSE Physics calculation. I’m sure the worksheet is far from perfect, it may well contain errors and I’m sure there’s many ways in which it could be improved. I think it took me about 30-40mins during some time in one of my school’s departmental meetings after we’d done some work looking at reducing cognitive load and ‘completion problems‘ as described in Ben Roger’s book. I’m pretty sure I created it by adapting an existing worksheet that was already in the lesson folder, I don’t know if this was made by a colleague or if it originated from somewhere online… so if you recognise any of the questions that will be why! I’m offering up this version in the spirit of ‘we’re all working on stuff like this, here’s my attempt, have a look, see what you think’. Any feedback welcome.

Here’s the link to the worksheet.

The worksheet is ‘faded’ in that it starts with lower demand questions which are partially completed, and then builds in additional steps and reduces the structure/scaffolding as the students work through.

If equations like F=BIL come up on the exam, I want students to follow a set procedure for doing the calculations. For me, this is:

  1. Circle/highlight all the numbers in the question
  2. Write down all the information given, changing units (e.g. cm to m) if needed
  3. Write the equation you think you need, in letters
  4. Substitute in the relevant numbers in the right places
  5. Then do the calculation (changing the subject first if needed, setting out your work properly “like in maths” – start a new line after each step, line up the equals signs vertically).

This follows the ‘substitute first’ approach; the exam board for the science GCSE I teach (AQA) promotes this approach by their marking policy (whereby correct substitution into an incorrect rearrangement gets no marks, but if you substitute correctly first and then rearrange incorrectly 1 mark is usually awarded for the substitution). Matthew Benyohai has discussed whether AQA’s policy is a good thing (or not) here.

So: the worksheet. Questions 1, 2 and 3 provide a model structure (with gaps) for students to complete basic calculations for F. Q4 adds in standard form. Q5 and Q6 then add in unit conversions including prefix conversions (milli, micro etc).

Then Q7-11 build in “changing the subject”, in addition to standard form and unit conversions – with gradually reduced levels of structure/scaffolding until Q10-11 when there is just a blank answer/working space.

For most classes, I would additionally set some of the grade 8-9 AQA specimen exam questions, specifically the 5-6 mark multi-step calculation questions. There’s one where they have to combine F=BIL with W=mg, and another where they have to use F=BIL along with the principle of moments. Students can really struggle with these, so I tend to work through (model) one as a class (using the visualiser) and set them the other. And also, at the end of Y11, during the revision period, teach a specific lesson (with its own, associated SLOP) about these 5-6 mark calculation questions.

It’s important to me that all of the practice questions actually get students to practice what they’ll need to do in the exam, this is why all the questions are ‘word questions’ where I expect students to complete all of steps 1-4. And I also prefer to have space on the sheet, just below each question, for students to do their working – just like in exams. Rather than a list of questions on one sheet of paper and then switching to the work being done on a separate sheet of paper/exercise books. Does this help ease the extraneous load? Maybe, maybe not. Possibly just a matter of preference.

In the exam, the equation (F=BIL) is given on the equation sheet. I get students to complete this worksheet with the actual exam equation sheet in front of them. Whilst they’re doing the worksheet, they should be looking at the equation sheet (not their books) every time they have to write out ‘F=BIL’. They need to learn/practice where to look to find this equation.

I agree with Adam Boxer that it would be helpful at the end worksheets like this to have some mixed / cumulative calculation questions, where students actually have to identify which equation to use, from all of the equations previously studied. Some of these Qs should need F=BIL. My sheet, as it currently stands, doesn’t get students to practice this skill as all the questions are all on F=BIL. In the past I’ve left practice of this skill until revision periods after I’ve finished teaching the course, but I think introducing this aspect sooner/regularly throughout the course would provide a nice opportunity for spaced practice/retrieval of previously studied/memorised content/eqns. Something to work on.

Finally… the last two pages of the worksheet are not to do with the F=BIL calculations, but some SLOP on the direction of the F=BIL force, i.e. Fleming’s LH rule. (OK so there’s only 5 diagrams, so maybe this is not SLOP but ABOP – a bit of practice. In the absence of SLOP, ABOP is better than nothing!). These 5 diagrams are for getting students to practice the single skill of using Fleming’s left-hand rule to identify the direction of the force, in isolation from the other ‘motor effect’ content. Hence why all the rest of the parts of the question are removed, leaving only the diagrams. No written instructions, I tell them what to do – these are the ‘you do’ following some ‘I do’ ‘we do’ modelling of this skill using other images.

All five of the diagrams are from specimen/actual exam papers – I think it’s useful to show students multiple different depictions of (essentially) the same experiment. Much like when my biology colleagues show students different diagrams/depictions of the heart, so they’re prepared for however the heart might be depicted on their exams. With the motor effect I think showing students multiple different ‘styles’ of diagrams of the same thing is also really useful to emphasise the essential features (deep structure?) of this content. And its also just good practice of using the LH rule, which is something a lot of students find tricky.

Any comments/feedback welcome here or via twitter.

 

note –

As I’ve been drafting this, Adam Robbins has written a similar post. Lots of similarities, some slight differences… happy to be adding my thoughts to the mix too.

 

 

Teaching Electricity; The Rope Model

This is a slightly adapted version of a post made on the #cogscisci mailing list.

Acknowledgements:

 

 

When teaching electricity at KS3, 4 and 5, I think there are six fundamental ideas which underpin most of any electricity topic. I think the first two should be pretty well covered in primary science, leaving secondary science to formalise the latter four.

  1. The idea of electricity involving a ‘flow’ (of … something… see 3!)
  2. The idea of a ‘complete circuit’ being necessary for the flow to occur (in a battery-powered circuit)
  3. The idea of charge (what flows in circuits)
  4. The idea of current (the rate of flow of charge)
  5. The idea of potential difference (the cause of the flow – ideas about how PD links to transferred energy should be developed much later in KS4 and 5 I think)
  6. The idea of resistance (a measure of the ‘opposition’ to the flow of charge)

 

Many people have discussed the importance of beginning an electricity topic with the concept of charge. Ben Rogers has a section in his excellent book (also here) about the importance of distinguishing the scientific meanings of this word from other ‘everyday’ meanings.

At my current school, we restructured our Y7 so students are taught the structure of the atom (it’s not hard, it’s pattern spotting, and Y7s love it!) twice, before they do their Y7 electricity topic  (once as an add-on to the end of the ‘particles’ topic, and then again in our Y7 ‘chemical elements/periodic table’ topic). That means they already know about protons, neutrons and electrons (in shells) BEFORE starting the electricity topic. Its then a much smaller cognitive jump to say that ‘in some materials, like metals, some of the electrons are free/delocalised’ (with the appropriate explicit vocabulary instruction for delocalised, of course!) – and then to say that ‘something called a potential difference has to be applied across the ends of a metal, to make the free electrons (which are already there, within the metal) flow’. Applying a PD across an insulator has no effect as there is nothing within the insulator which can flow (no mobile charge, no free electrons, all electrons are bound). 

However, the main subject of this post is to write about the use of different models in the electricity topic, which are essentially the different ways we are teaching students to picture/think about electricity.

There’s discussion amongst physics teachers about whether its helpful or not to present students with numerous different models or electricity. From a CogSci point of view you could argue that multiple models unnecessarily increases cognitive load. Lots of physics teachers (including Ben Roger’s excellent book) disagree, which is fine. The argument given is that its good for students to evaluate the strengths and weaknesses of different models. But, I think students can only do this [evaluate models of electricity] when they already have a good understanding of the physics that is being modelled. If you teach electricity by saying  ‘electricity is like X’ but then ask ‘Right – now I want you to think about how electricity is not like X I think students will struggle – as you’re confusing the fragile new schema which they’ve tentatively been building about this topic they don’t know much/anything (technical) about yet.

In the past I’ve seen (and certainly, taught myself too!) lessons where a teacher has explained/demonstrated a model to ‘explain circuits’ and then immediately asked students to evaluate the weaknesses of  the model – they can’t do it because they don’t yet understand electricity well enough to understand what aspects of electricity the model shows well and what aspects are not shown well. I’m not saying this kind of model-evaluation activity is impossible to do, I just think it’s often performed far too early before students have developed good enough ‘electricity-schema’ to be able to evaluate the models effectively.

Secondary to this, I’d argue the point of the electricity topic is to teach students how electricity works; I think teaching students different models of electricity and their strengths and weaknesses has the potential to slightly side-track the point of the topic. If you were writing a list of what you want students to know by the end of the electricity topic, I doubt you’d include statements like “in the ‘water model’ of electricity a battery potential difference is modelled by a difference in fluid pressure“. But I’m sure you would include something like ‘In a circuit, a potential difference is required, to cause the charge/free-electrons to flow‘. Fundamentally, the core knowledge we want students to gain is about electricity itself, whereas knowledge of various electricity models is, to me, distinctly secondary.

I feel there is a danger that students (and teachers – especially non-specialist teachers of physics) might end up spending too much time thinking about the different models rather than thinking about electricity itself. This is important because, as we know from Willingham (and elsewhere), what students are thinking about is really important as that is what they’ll remember. If they spend too much time thinking about comparing ropes and waterpipes and trains/carriages this could run the risk of diverting attention from thinking directly about electricity and how electricity works.

So – the focus of the electricity topic should be on how electricity works (duh!). Any models/analogies referred to should clearly illustrate/be analogous to/help students to ‘see’/accept what happens within circuits. So what models should you use? I (and, from what I understand, also the Institute of Physics) happen to prefer one model in particular – the rope model – I’d like to take the opportunity to explain why.

With water models – students end up thinking that when you add a parallel branch to a circuit, the original water (current) then splits. This is incorrect. When you add a parallel branch to a circuit, additional current now flows and it is this new, greater current that splits at junctions in parallel circuits. In the water model, adding a parallel branch isn’t like adding an extra (empty) pipe, its like adding an extra pipe-that’s-already-full-of-water – so there’s now more water flowing in the circuit. Whilst some students ‘get’ this, I find that what was a quite simple model has not become a bit complicated. I’m also not sure it’s intuitively obvious that the ‘current’ (rate of flow of water) increases in the ‘return to the battery’ part of circuit when the two parallel paths rejoin.

Radiator models – have the same issues as water models. Also –do students really understand central heating systems well enough to use them as a reference for understanding electricity? I’d argue not.

‘Donation’ or ‘carrier’ models – these are like @emc2andallthat‘s CTM model – which, admittedly, is excellent at showing some aspects and developing quantitative reasoning. Another common ‘donation’ model is the teacher handing out tokens/sweets (energy) to students (charge) walking around the classroom, which are then ‘dropped off’ at bulbs.

I think there are many issues with donation models…
  • How do the charges know how much energy to drop off at each bulb? Answer – they don’t – because this isn’t how the mechanism of electrical energy transfer (electrical working) works (see the ‘rope model’ for what I think is a better explanation/demonstration of this)
  • What happens to the energy in the loaded carts if the flow suddenly stops? I don’t think it’s helpful for students to picture the energy still being there in the wires on one half of the circuit, but not on the other half of the circuit.
  • Donation models imply there is a difference between the charges on either side of the circuit. There isn’t, really. Energy is just a number you calculate, and not a real thing that can be ‘carried’.
  • AND – how do you explain AC?  mains electricity – arguably the most common way electricity is encountered by students in everyday life – is left as a total mystery!

The rope model – a bad way to do it

I’ve realised over the last few weeks that when some teachers hear of the rope model they picture 10-20 students all holding onto a rope loop at different points. This is not a good way to do it – they’ll all be gripping and pulling on the rope, either gripping too hard to disrupt the demo or pulling too hard in response the person next to them gripping the rope. The teacher ends up having a battle just to get the rope to do what s/he wants it to do. Also – in terms of CogSci – they’re probably thinking about gripping the rope or not getting a rope burn, rather than paying attention to the things you (the teacher) wants them to pay attention too.

The rope model – a much better way to do it.
  • You need a loop of rope. Tie a length of rope (say, 3m) into a loop. Or even better – with a nylon rope, you can melt the ends together – so there is no knot that gets in the way.
  • Ask for one student volunteer. They are the bulb. Get them to barely grip the rope at all – with only one hand – so the rope slips through easily.
  • The teacher is the battery – they “provide a potential difference” by making the rope circulate. Ask students where the current started flowing first. Everywhere at once!
  • The rope should be speckled – the free electrons are already there, in the metal wires of the circuit. They all start moving at once, with the same (speed) rate of flow everywhere around the loop.
  • Direct students attention to the part of the rope close to your “bulb” – the rope travels no faster towards them than away from them. The rate of flow – the current – is the same everywhere in the circuit.
  • What is happening to the “bulb’s” hand? It’s getting hotter. Energy transfer is occurring – the battery’s store of energy is decreasing, the thermal store of energy at the bulb is increasing – but not because one side of the rope is ‘carrying energy’ to the hand and the other side of the rope is returning (‘empty’) to the battery – energy is being transferred by the circulation of the system as a whole.
  • How long did it take from the PD being applied (the teacher pulling the rope) for energy to ‘get’ to the bulb? No time at all – as soon as the rope starts circulating, energy is transferred. You don’t have to wait any time at all for charge to ‘carry’ energy around the circuit – because energy is not transferred from battery to bulb by charges ‘carrying’ energy; rather, energy is transferred by the motion of the system as a whole.
Then
  • Model the effect of increasing PD (pull the rope faster) – you get a greater rate of flow (current).
  • Model the effect of increasing circuit resistance – either get your “bulb” to grip the rope tighter, or invite 1 or 2 additional “bulbs” to come up and add their resistance (grip) into the circuit – the current (rate of flow) decreases. Where does it decrease? Everywhere – not just at the place with more resistance.
  • Get 2 “bulbs” in series to each grip the rope – one tightly (high resistance), one very loosely (low resistance). The current might be different now, but its still the constant all around the circuit. Whose hand gets hotter – where is more energy transferred? At the high resistance bulb. Did the rope have to know to “drop off” more energy there? No – its just obvious that more energy ‘input’ to the system is transferred there, rather than the low resistance bulb.
  • Make a parallel circuit by adding an entirely new rope loop (and bulb) into the system. The battery provides the same PD to both loops. Whilst both loops might circulate at the same speed (which, in circuits, is certainly not always true) it is obvious that where the rope loops ‘overlap’ in the shared part of the circuit (just “after” the battery, and where the parallel loops ‘rejoin’ just before the “battery”) that there is now more charge flowing than before – a greater rate of flow of charge. It should also be reasonably clear that the current in the original loop is exactly the same as it was before.

 

  • FINALLY – show alternating current (mains electricity – arguably the most common way electricity is encountered by students in everyday life) by constantly changing the direction of the loop motion. Energy is still transferred across the circuit, from the AC source (teacher) to the “bulb” (student’s hand) – but without any part of the rope having to travel from the AC source around to the bulb (to “deliver”) that energy.

 

I’m glad that people have found the above useful. I’m not presenting the Rope Model as a ‘silver bullet’ that will suddenly enable all to understand electricity – I just thought it might be useful to share a detailed description of my approach to using the rope model to provide a visible demonstration/analogy for tricky electricity concepts. Please do read the above in conjunction with the CTM model and the Supporting Physics Teaching materials from the IoP and make up your own mind about what will help you teach concepts in electricity best, to your classes.

 

 

Additional note –

It was suggested to me that one advantage of ‘carrier/donation’ models over the rope model, is donation models show electric potential and potential difference (the difference between one side of the circuit and the other) really clearly – but the rope model doesn’t show this very well at all.

I would agree that the rope model doesn’t show the idea of electric potential very well (i.e. intuitively) – but I think the rope model could show this. If you point at the ‘speckles’ on the rope and say they represent electrons, you could point to an arbitrary section of rope (say 10cm long – mark off this section on the rope with a sharpie if you like) and say ‘this section represents 6 billion billion electrons – one Coulomb of charge’. When that 1C passes through a “bulb” (hand gripping the rope) – you could ‘pause’ the flow and talk about the energy that was transferred by that one Coulomb of charge as it flowed through the ‘bulb’ – this ‘energy transferred/work done per Coulomb’ is the PD across the bulb.

OK – admittedly that’s not very easy/intuitive to understand and it doesn’t show a ‘difference’ between the two sides of the bulb, but it is possible to model PD in the rope model.

About that ‘difference’ between the two sides of the bulb. This is a difference in electric potential. Electric potential is a scalar field, a numerical property of every distinct point in space, due to the electric field at that point in space. (Temperature is an easy to understand example of a scalar field – we can model every point in a room (every x,y,z coordinate) as having a numerical value associated with it, which is the temperature at that point). The electric potential at a point in space tells you the stored energy that would be associated with every Coulomb of charge present at that point (energy per unit charge). This is a calculated number only and not representative of any physical difference between the electrons (charge) either side of the bulb. Yet – in carrier models, we are embedding a very clear picture of a physical difference between the charges on one side of a bulb and the other. That’s what I personally prefer not to do, and why I prefer not to use ‘carrier’ model even to get across the idea of PD. The ‘potential difference’ across a bulb is not a physical difference between the electrons on either side of the bulb, it is a difference in a calculated quantity associated with the points in space ‘in the wires’ on one side of the bulb and the points in space ‘in the wires’ on the other side of the bulb. (This is getting close to the limit of my understanding of circuits… if I’m outright wrong about any of this, do let me know…)

So what do I do instead to ‘get across’ the idea of PD? I use different coloured highlighters to highlight circuit diagrams to show parts of the circuit (different points in space) where the electric potential (the energy-per-unit-charge associated with 1C being stored there) has the same and different values. I’ll have to explain this in a separate blog post, another time! Thank you for reading.

 

Additional note 2 – some further reading…

Here’s an article that goes into the ‘donation model’ misconception in far more detail.

And here‘s another related article.

Physics Problems, Physics Questions, and the aim of School Physics

This post is about the language used to describe physics questions. Sometimes, physics questions are called ‘problems’. I’ve sometimes found this a bit weird, and I wanted to explore why. I’m not quite sure if this post is just a lot of “pedantic semantics” without any real impact or ‘message’ for practice … but I quite enjoyed writing it so here we go anyway.

This was prompted by reading Ben Rogers’ excellent book, “The Big Ideas in Physics and How to Teach them“. I think this is a great book, I would say his writing in Chapter 0 (about how Cognitive Load Theory can be applied in teaching secondary physics) should be required reading for all physics teachers.

Ben opens the introduction to his book with a quote from Feynmann: “Know how to solve every problem that has been solved”. Yes – absolutely!

Ben goes on to say that being a physics teacher involves teaching students “how to be physicists“. I’m not sure I fully agree with this – I think teaching someone how to be a practicing physicist (e.g. a post-doc or a research physicist) is slightly different to what we do in school physics (Rosalind Walker has discussed this a bit here).

Ben goes on to say that teaching students how to be physicists “means teaching students how to become physics problem solvers” and then “to become a better problem solver, a novice physicist needs to be exposed to as many archetypal questions as possible”. This makes total sense – knowledge (of content, and of exemplar questions and their answers) precedes skill, and solving problems (thinking) is memory in disguise – solving problems involves retrieving appropriate already-known ideas into working memory and then rearranging/comparing them in the right way (as discussed in Willingham ch4).

But: did you notice Ben’s shift from problems to questions? On my reading, I’m not sure as to whether he’s using “Physics problems” interchangeably with “Physics questions” (and also, it probably doesn’t really matter!). That said, having thought about it a little bit, I don’t think these terms are interchangeable, I think there is a distinction between the two. I think Physics problems are a subset of physics questions.

Here are some physics questions which (in my opinion) are not physics problems:

(1) State what is meant by internal energy. There is no ‘problem’ to be ‘solved’ here, the answer is just a statement which the student will either know or not-know. Pure declarative knowledge.

(2) Explain how a skydiver reaches terminal velocity. There is no problem to be ‘solved’ here. Answering this question does not involve a ‘problem-solving’ process. This is an archetypal question with an well-known archetypal answer/explanation which the student should know.

(3) Describe the properties of alpha, beta and gamma radiation.
(4) Describe what happens to a nucleus during beta decay.
There are no problems to be ‘solved’ here. Answering these questions does not involve a ‘problem-solving process’, they involve a student retrieving and setting out some knowledge which (hopefully) has been learnt.

So, if these are not physics problems, what makes a physics problem then? I’m not sure the distinction is black and white, I think the boundary between physics questions and physics problems is probably a bit of a fuzzy grey area, but I think you can still give examples from either end of the spectrum to illustrate the distinction.

Physics problems probably tend to involve being given a situation and then being asked to work something out, making use of what has been taught. Maybe this is just the distinction between AO1 (recall) and AO2 (application) – hence my feeling that maybe this post is just something everyone knows already…

So here are some example ‘problems’:

(A) from the GCSE AQA SAMs:

Capture2

(B) – adapted from a previous specification past exam question:

Look at the information in the table. Which energy-saving method should the householder install?

insulation q

And (C): just to show that not all physics ‘problems’ involve calculations:

A factory produces different thicknesses of metal sheets, from 1mm to 2cm thick. To monitor that the metal produced is the correct thickness, a radioactive source is placed on one side of the sheet and a detector on the other side of the sheet. The output from the detector should tell factory workers whether the card produced is too thick or too thin.

Which radioactive source should be used? Choose from the table below and explain your choice.

radiation q

 

So – I’d say that: all physics problems are physics questions, but not all physics questions are physics problems. Here’s a Venn diagram (because, who doesn’t love a Venn diagram):

Capture3

So… the purpose of secondary-school-physics: where Ben says that school physics teaching is about teaching students to become physics problem solvers, I would broaden this. I would say that the primary focus of secondary school physics is teaching students how to become great physics question-answerers.

Whilst this might seem a bit ‘robotic’ / exam-factory-ish, the blunt fact-of-the-matter is this: to succeed in physics education students have to learn (be taught) how to answer physics questions (for GCSE and A-level exams). I’ve often heard it said at my current school that “the best pastoral care for students is a great set of exam results” (which opens doors for them in the future). To get a great set of exam results, students have to be able to answer the exam questions, and to be able to answer the exam questions, you need great domain-specific-knowledge.

So, as many others have said before me, secondary school physics time should be spent on

  • developing knowledge/schema:
    • knowledge (and understanding) of the core physics content
    • knowledge of common types of questions/problems that get asked
    • knowledge of how to answer them
  • explicit teaching of memorisation techniques
  • explicit teaching of ‘how to answer these kind of questions in this topic’
  • explicit teaching of ‘what you should be thinking if you get these kind of questions’ (I think this pretty much sums up what metacognition should often look like in secondary school science)
  • and, of course, shed-loads of practice (including retrieval practice).

 

Although earlier I said that the primary focus of secondary school physics is teaching students how to become great physics question-answerers, this clearly isn’t an end-in-itself. The physics-knowledge and the physics-skills (and also, hopefully, a love/enthusiasm for physics too) are the real end goals of physics education. But the reality of day-to-day teaching should focus on the purpose of getting students to become great physics question-answerers  and the route to this goal is great physics knowledge and shed-loads of practice.

So – how best to teach that knowledge and develop that schema? That’s where great teacher subject-knowledge comes in. I am lucky to work one day a week for the Institute of Physics Stimulating Physics network as a Schools Physics Coach, that means I visit local schools to run teacher CPD sessions on developing teacher physics subject knowledge and physics subject-specific pedagogy. The Institute of Physics has built up a national network of such physics coaches, and the support is free to any state-funded school who signs up. Do visit http://www.stimulatingphysics.org/ to find out more.

 

Disclaimer: although I currently do some work representing the Institute of Physics, this blog represents my personal opinions/recommendations only and is not affiliated to, or representative of, the Institute of Physics.