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# Language issues for teaching electricity

## 'Batteries' and 'cells'

Most everyday batteries are rated 1.5 V. This is because the chemical reactions that are used in modern alkaline batteries happen to produce about 1.5 V.

Strictly speaking a single 1.5 V battery should be called a ‘cell’. Many cells joined together form a battery. You can also buy 9 V batteries. These are simply six 1.5 V cells that are connected in series inside the battery case. We have invented a non-standard 3 V battery (notionally made from two 1.5 V internal cells) for our animations simply because 3 is an easier number than 1.5.

I'm not too pedantic about the difference between ‘battery’ and ‘cell’ since there are no important conceptual misunderstandings associated with it. You may want to explicitly identify the difference between an electrical cell and a cell in biology.

## 'Charge'

Physicists tend to be quite casual about using the word 'charge' as shorthand for 'a charged thing', like an electron.

When I refer to charges in these lessons I normally mean conventional charges i.e. 'lumps of one coulomb of imaginary positive charge'.

I would suggest referring to charges and clearing up misunderstandings as they arrive. The disadvantage of using the more correct term 'charge carriers' is that we are now telling students (correctly) that our moving particles are carrying both charge and energy, which could lead to confusion.

## 'Converting'/ 'changing'/ 'transferring'/ 'shifting' energy

Is energy real or is it just a useful fiction?  Richard Feynman was of the view that

It [the conservation of energy] is not a description of a mechanism, or anything concrete; it is just a strange fact that we can calculate some number and when we finish watching nature go through her tricks and calculate the number again, it is the same.

Now there are lots of different ways of calculating this energy number depending on whether you're interested in how much damage a car crash will cause, how long it takes a kettle to boil or how big a bang a nuclear explosion will make.  Because we can calculate energy in several different ways we come up with this idea that energy comes in different forms.

This is why we can use ideas like energy 'changing' or being 'converted' from one form into another.  When we write something like 'Potential energy lost = kinetic energy gained' we're using this idea of change.

However some educationalists argue that it's confusing when energy is first introduced to talk about these different ways of calculating it.  Their approach is that there's this single idea called energy and all we do is move it from place to place.  In this case they prefer to talk about energy being 'transferred' or 'shifted'.

## Current 'in' or current 'through' a component

This is a slightly nit-picking point.  Some people say that current doesn't 'flow'.  The charges that make up a current 'flow' but the current itself doesn't.  For those who insist on this point it makes sense to talk about the current 'in' a component.

However I prefer to talk about the current 'through' a component because it gives a little extra reminder that current is to do with movement.

## Current 'splits' at junctions

This is a very common way of explaining parallel circuits but you need to be extremely careful with it.

The first problem is that it reinforces the notion that electric current starts from the battery and then travels along empty wires until it comes to a junction and then splits.  As we know the wires are already full of charges and they all start moving very slowly everywhere at the same time.

The second and more important problem is that it reinforces the constant current misconception.

## 'Electricity'

I try to avoid using this word except as a description of the subject area. I prefer to talk about more precise ideas of electrical energy, charge, etc.

## 'Energy'

Energy is often defined as ‘the ability to do work’ but the meaning and use of the word is subtle and not without controversy.  Energy is a bit like money.  It tells us how much certain jobs cost and how much we’ve got to spend.  It can help us answer questions like 'Have I eaten enough to climb this mountain?' or 'How long can this battery light this bulb for?'.

Just like money it can only be saved or given to someone else. (If you’re an economist please ignore the ‘lump of wealth’ fallacy inherent in this analogy). You can only really get a feeling for the idea of energy through use and I would not try and nail down an exact definition too quickly.

## '...from positive to negative' (or vice-versa)

There are two ways that teachers subtly reinforce the incorrect idea of charges flowing through empty wires from battery to component: the language they use and the way they indicate on a diagram.

I would recommend using the phrase ‘in the sense positive to negative’ if you mention direction of flow and would suggest adding ‘very slowly everywhere at the same time, like a wheel’ as often as possible.

When indicating on diagrams use both hands to make a wheel shape rather than pointing from the battery to the component. If you are drawing charges on your diagram you may even want to fill them in randomly rather than starting from the battery.

## 'Heat' and 'internal energy'

Heat is often used to mean something like 'the total movement energy of all the particles that make something up'.

Strictly speaking this is not quite right.  This random motion should be called 'internal energy' and 'heat' should only really be used to describe the movement of energy from one thing to another.  I don't normally make such a fine distinction and am quite happy to talk about heat as the random movement of particles.

## 'Power' supply

In physics, power means how quickly energy is converted. Power supplies should really be called energy supplies but this would probably cause more problems than it solves.

## 'Quicker'/ 'slower'

Even when we move on to ideas about power, it is probably still worthwhile talking about things converting energy 'quickly' or 'slowly'.

Use 'more' and 'less' when you talk about the total amount of energy converted. e.g. A hot oven converts energy quicker than a cool one but more energy might be converted if I leave a cool oven on all day than if I leave a hot one on for a few minutes.

## 'Voltage', 'Potential' and 'Potential Difference'

'Voltage', 'potential' and 'potential difference' are all to do with energy.

If you think in terms of our animation, 'potential' at a point means 'how much energy (red stuff) does a charge have at this point in the circuit?'.  'Potential difference' between two points means 'how much energy (red stuff) does a charge lose going from this point to this point?'.

Potential and potential difference are quite strictly defined and are the more scientific terms.

A slightly more informal approach is to refer to 'voltage at this point' or 'voltage across this bulb / between these two points'.  I tend to talk about 'voltage' rather than 'potential' to start with, for simplicity's sake.

The term 'amperage' to refer to current is generally frowned on by physicists but not so much by technologists.

## Voltage as a 'push'

This is a perfectly reasonable going-in position for the meaning of voltage and nicely ties in the idea that big voltage means big current.  However it's a bit of a dead-end concept in some ways because it's not easily linkable to energy.  This means you can't extend the idea to talk about how voltage is shared around a series circuit and there's no particularly intuitive link to the formula for electrical power.

I use the idea only rarely and prefer to talk about voltage in terms of energy, which is how it's actually defined.

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