IoP Energy: It’s About The Physics, Stupid!

[I]t is ambition enough to be employed as an under-labourer in clearing the ground a little, and removing some of the rubbish that lies in the way to knowledge;- which certainly had been very much more advanced in the world, if the endeavours of ingenious and industrious men had not been much cumbered with the learned but frivolous use of uncouth, affected, or unintelligible terms, introduced into the sciences

John Locke, An Essay Concerning Human Understanding (1690)

OK, so I was wrong.

In a previous blog, I suggested a possible “diagrammatic” way of teaching energy at GCSE which I thought was in line with the new IoP approach. Thanks to a number of frank (but always cordial!) discussions with a number of people — and after a fair bit of denial on my part — I have reluctantly reached the conclusion that I was barking up the wrong diagrammatic tree.


The problem, I think, is that unconsciously I was too caught up in the old ways of thinking about energy. I saw implementing the new IoP approach as being primarily about merely transferring (if you’ll pardon the pun) the vocabulary. “Kinetic store” instead of “kinetic energy”? Check. “Gravity store” instead of “gravitational potential energy”? Check. “Radiation-pathway-thingy” instead of “light energy”? Check.

Let’s look at the common example of a light bulb and I will try to explain.

Using the old school energy transfer paradigm, we might draw the following:


In spite of its comforting familiarity, however, there are problems with this: in what way does it advance our scientific understanding beyond the bare statement “electricity supplied to the bulb produces light and heat”. Does adding the word “energy” make it more scientific?

For example, when we are considering “light energy”, are we talking about the energy radiated as visible light or the total energy emitted as electromagnetic waves? It is unclear. When we are considering “heat energy” are we talking about the energy emitted as infrared rays or the increase in the internal energy of the bulb and its immediate surroundings? Again, it is unclear.  In the end, explanations of this stripe are all-too-similar to that of Moliere’s doctors in The Imaginary Invalid, who explained that the sleep-inducing properties of opium were due to its “dormative virtues”; that is to say, sleep was induced by its sleep-inducing properties.

The problem with the energy transfer paradigm is that it draws a veil over the natural world, but it is a veil that obscures rather than simplifies.

The IoP, after much debate, collectively rolled up its sleeves and decided that it was time to take out the trash. In other words, they wanted to remove the encumbrance of terms that had, over time, essentially become unintelligible.

The new IoP model distinguishes between stores and pathways. For example, an object lifted above ground level is a gravity store because the energy is potentially available to do work. Pathways, on the other hand, are a means of transferring energy rather than storing energy. For example, the light emitted by a bulb is not available to do work in the same sense as the energy of a lifted weight. It is, within the limits of the room containing the bulb, a transient phenomenon. Many photons will be absorbed by the surfaces within the room; a small proportion of photons will escape through the window and embark on a journey to Proxima Centauri or beyond, perhaps.

Now let’s look at my well-meaning diagrammatic version of the energy transfers associated with a light bulb:


The stores are “leak-proof buckets” holding the “orange liquid” that represents energy. The pathways are “leaky containers” that enable energy to be transferred from one store to another. I have to admit, I was quite taken with the idea.

The first criticism that gave me pause for thought was the question: why mention the thermal store of the bulb? Surely that’s a transient phenomenon that does not add to our understanding of the situation. Switch off the electric current and how long would the thermal store be significant? Wouldn’t it be better to limit the discussion to two snapshots at the beginning (electrical pathway in) and end (radiative pathway out)?

The second question was: what does the orange liquid in the pathways represent? In my mind, I thought that the level might represent the rate of transfer of energy. Perhaps a high power transfer could be represented by a nearly full pathway, a low power transfer by a lower level.

But this led to what I thought was the most devastating criticism: why invent objects and assign clever (but essentially arbitrary) rules about the way they interact when you could be talking about real Physics instead?

Is there any extra information in the phrase “light energy” as opposed to simply the word “light”?

Efficiency of a bulb: find the total energy emitted as visible light and divide by the total energy emitted as light of all wavelengths.

And that’s when I realised that I wasn’t helping to take out the trash; in fact, I was leaving the rubbish in place and merely spray painting it orange.

Now don’t get me wrong, I think there’s still a long road ahead of us before we become as comfortable with the IoP Energy newspeak as we were with the old paradigm. As a first step, I suggest all those interested should read and contribute to Alex Weatherall’s excellent Google doc summary to be found here. But I honestly believe that it’s a journey worth taking.

Opium facit dormire.
A quoi respondeo,
Quia est in eo
Vertus dormitiva

— Moliere, The Imaginary Invalid (1673)

14 thoughts on “IoP Energy: It’s About The Physics, Stupid!

  1. paulmartin42 March 11, 2017 / 5:58 pm

    via Goofle translate:

    Opium causes sleep.
    A single answer,
    For in him
    vertus sleeping

    & wikipedia returns something about Quack medical answers/cures & elan_vital

    Hope this helps you on your way ….

    • e=mc2andallthat March 12, 2017 / 11:25 am

      I think the quote is actually meant to be in bad, nearly incomprehensible Latin as Moliere was satirising the doctors of his day…

  2. Miss Ironfist March 11, 2017 / 8:46 pm

    “I was barking up the wrong diagrammatic tree.”

  3. IanH March 11, 2017 / 10:21 pm

    Really useful thoughts – thank you for sharing them. The focus on the ‘real’ physics – not the hand-waving of the old language – is indeed the aim. Yes, it leads to the maths which is the whole point of discussing energy, but trimming it as much as possible is helpful.

    I’d add one thing; the time spent considering the thermal store of the filament as an ‘interim’ stage isn’t wasted – for *teachers*. I think I’d keep it in reserve when working with students, because someone is sure to ask, but as you say, it’s easier to focus on different start and end ‘snapshots’. (We don’t measure the temperature of the filament, do we?) It’s the usual story that we as teachers need to be a step ahead of (or a level deeper than) the kids…

    • e=mc2andallthat March 12, 2017 / 11:12 am

      Thanks, Ian! The more I think about this, the more I realise I haven’t thought about it enough. It’s going to take some time before I’m fully comfortable with the “Newspeak”…

  4. paulmartin42 March 12, 2017 / 7:10 am

    Let me focus on the light bulb. The tech has moved on from filament lamps & there is so much in the discharge tube & now LEDs. I am not sure that you want to complicate thermal store theory with (my) practical experiments with various GU10 (ie small tungsten halogen reflector lamps) but in my kitchen science work I am fascinated by how much heat is radiated by alternative configurations – as were, to my surprise, an Elgin school at a recent Go4Set competition.

    I am betraying my engineering background when I wonder whether there is loads more (complex?) real world (eg phosphor lines) in your diagram of bulb efficiency. Lights are the most prolific domestic appliance & (as an aside) I am astonished that a party balloon battery powered LED is still glowing 3 months since Christmas – samples wildly reduced at your local Tesco Extra.

    • e=mc2andallthat March 12, 2017 / 11:23 am

      You can see what I think is the line emission spectrum due to the phosphor coating — or is that the (visible part of the) line emission spectrum of the ionised gas? — when you look at a discharge tube through a hand-held spectrometer, of course. I haven’t tried a halogen lamp yet, but I understood they were a fair bit more efficient than filaments.

      Technology marches on. I still haven’t quite recovered from not being able to talk about CRTs…

      LEDs frequently make me think of Clarke’s law that “Any sufficiently advanced technology is indistinguishable from magic”

  5. @SteveTeachPhys March 12, 2017 / 11:25 am

    There’s so much to take issue with here, and none of it is your fault!

    1. The IoP introduced orange liquid, it’s all over their explanations on Talkphysics. Is newspeak being refined? Are more concepts being removed because they risk wrong thought?
    2. Do I think light energy adds more than light? Well yes, a tiny bit, it helps bring home the idea that nothing is without cost and that energy is the accounting tool used. I certainly think it adds more than Light Pathway. I do agree that considering the “internal energy of the filament” is of no help whatsoever.
    3. As I said in comment in your last blog, does anyone know whether the exam boards plan to go Newspeak 2.0?
    4. The lightbulb is ‘the example’ on the old spec because we needed to explain why they were being phased for energy efficiency reasons. We’re going to struggle to even begin that conversation under newspeak. Now it might be a good thing that we can’t discuss light emitting devices, who the hell wants to explain LEDs to Y10? Unfortunately lightbulbs are still in there as examples of non ohmic devices so we have to talk about them.

    I think a way out may be a quantitive one. If we and the thought police agree that we can discuss pathways in terms of power, then we do efficiency Calcs for things like the lightbulb in watts, electrical power, power in the respective light and heating pathways etc. Meanwhile we avoid any kind of “language only” examples where the aim of the device is a pathway and not a store. For example we might talk about microwave ovens, but not mobile phones. Self editing is after all in the spirit of newspeak!

    • e=mc2andallthat March 12, 2017 / 11:59 am

      Thanks, Steve. Yes, the IoP introduced orange liquid, but they apparently don’t like to see it being sloshed between stores. Their view is that it is more productive to look at the actual Physics involved (e.g. conduction, convection, radiation etc).
      I think you’re actually right about light energy as far as thinking about conservation of energy is concerned; but then again, does “light energy” refer to visible light or to the whole e-m spectrum? It’s used in many ways by different people so I can see the argument for amending the vocabulary.

      The exam board position is still unclear as far as I know, but I would hope they would not penalise oldspeak. A suggested energy question that I have heard broached is “A second identical bulb is added in parallel to a circuit with a battery. Discuss what happens to the useful life of the battery.”

      I am still not fluent in energy Newspeak myself, but I think the “thought police” would approve of “stores in joules, pathways in watts” and an emphasis on the quantitive rather than the qualitative seems to be the way to go. Your example of the microwave oven vs the mobile phone is fascinating — how do we talk about that?

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