Current – An Argument for Many Models

Current is a nice simple word; it means the rate of flow of charge. So you need to explain rate to get a proper understanding. And there are two parts to rate: the velocity of the charge, and the amount of charge per unit volume. So you need to explain what the amount of charge per unit volume is….


Continue reading “Current – An Argument for Many Models”


Electricity’s Colourful Past

Yesterday I wrote about electric charge and its confusing meanings (here). I had intended to write about voltage and current today, but after a discussion with Mary Whitehouse @MaryUYSEG and a troubled night’s sleep, I’ve decided to write about the word electricity instead. Much of the information in this blog is taken from Iwan Rhys Morus’s (@irmorus1) brilliant book: Shocking Bodies.

Among physicists, the word electricity has lost it’s usefulness. Instead, it is rather a nuisance: an idea with a colourful past. But that past is glorious.

Electricity’s colourful past

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Electric Charge – why it is difficult to understand and how to help.

My heart has never been in definitions. It was set against them in Africa 20 years ago, when I was teaching physics in Ghana. The exams, and the students, prioritised the recall of definitions. And I didn’t know them – I just converted the equation into words (I=Q/t Definition: current is the rate of flow of charge). 

When my definitions disagreed with the examboard’s definition, I saw doubt, fear and sometimes anger on the faces of my students. So I learnt the exam board’s definitions, sadly, not with good grace.

Recently, I have begun thinking about definitions again. I often see teachers asking students to write their own definitions as either a warm-up or assessments task. But I think this is too hard. If you want students to learn a definition, learn the exam board one.

But definitions are not the key to understanding a concept. Daisy Christodoulou’s new book (Making Good Progress) quotes Thomas Kuhn when talking about definitions. She (and he) make the point that a definition doesn’t lead to understanding: repeated exposure to the concept through discussion, models and texts; solving the discipline’s standard questions about the concept and carring out the standard practicals leads the learner to a rich understanding. Then the definition becomes useful. Continue reading “Electric Charge – why it is difficult to understand and how to help.”

Using Comparative Judgement to Rank the Importance of Concepts

If you haven’t heard of comparative judgement (CJ), it is the latest fashionable way for judging the quality of student work (see here and here) – although it’s not really new. I think it has great potential for judging longer written answers (or even short answers) beyond just right and wrong – some right answers (and some wrong answers) are better than others and this should be recognised and explored.

I had the idea of trying our CJ by ranking energy statements into order of importance for understanding energy. I took the statements from the ASEs Big Ideas in Science energy section here.

10 physics teachers ranked the statements using the CJ engine at Making 25 comparisons (each comparison taking, on average, less than 10s), the correlation was surprisingly high (0.82). The top 5 are:

  1. When energy is transferred from one object to others the total amount of energy in the universe remains the same; the amount that one object loses is the same as the other objects gain.
  2. Energy cannot be created or destroyed.
  3. Objects can have stored energy (that is, the ability to make things change) either because of their chemical composition (as in fuels and batteries), their movement, their temperature, their position in a gravitational or other field, or because of compression or distortion of an elastic material.
  4. An object at a higher temperature heats the surroundings or cooler objects in contact with it until they are all at the same temperature.”
  5. The transfer of energy in making things happen almost always results in some energy being shared more widely, heating more atoms and molecules and spreading out by conduction or radiation.

The full bank of statements, ranked, is here.

I’d be really interested if anyone has tried this with written exam answers.


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