not just described, Explained

Home

Misconceptions quiz

Subscriptions FAQ

### Physics

Physics subscription prices

### PSHE

PSHE subscription prices

# Why use conventional current?

## What is conventional current?

Conventional current says 'whatever's really happening in a circuit, we'll pretend it's positive charges moving in the sense positive to negative'.

This means if electrons are flowing from left to right we'll just imagine replacing them with positives moving in the other direction.

Here are some of the reasons why Furry Elephant uses conventional current rather than electron flow.

## Explaining conduction in liquids and gases

Some forms of conduction (for example in liquids) involve the flow of positive charges in one direction and negative charges in the other.

We still only have one lot of current because each ion only makes 'half' a journey.  We have to define current as flowing only in one direction in liquids not in both directions.  (If it flowed equally in both directions then it would add up to zero and current would not be conserved around a circuit).

In order to understand the idea of current flow in liquids we have to imagine that real negative charges flowing in one direction can be replaced by imaginary positive charges flowing in the other (or vice-versa).

This means we have 'two halves make a whole', rather than 'two halves cancel out'.  So we have to deal with imaginary charges otherwise we can't teach current flow in liquids and gases properly.  If we have to develop this 'replace with imaginary charges' concept we might as well replace the right ones.

## Telling a consistent story about energy

The reason why electricity is important is that it helps us do lots of jobs.  The environmental impact of electricity is to do with the way this energy is converted from other forms.

Transfers of electrical energy involve the movement of charge from high potential energy (voltage) to low potential energy (voltage).  Electrical potential energy is defined in terms of the movement of positive charge.  I know it's irritating but that's the way it's defined.

The positive terminal of a battery is at a higher potential than the negative terminal.  Moving from positive to negative involves a release of energy.

If we want to use electron flow, we have two choices:

i.  We say that the negative terminal of the battery is at a higher voltage.

This is wrong.  Potential is not defined like this and we are teaching something that is wrong, where the correct version is understandable.  It's also confusing for the negative terminal of a battery to be 'higher' than the positive.

ii.  We say that the positive terminal of the battery is at a higher voltage.

This is true.  But we can only consider positive things rolling down this hill.  If we think about negative things then they roll 'up hill', which we know can't be right.

The only way it can work is that the real negatives flowing in one direction are replaced with imaginary positives flowing in the other.

## Supporting non-specialists who teach physics

Furry Elephant aims to support non-specialists who teach physics.  Our experience is that many non-specialists have problems with the idea of conventional current.

We occasionally receive rather indignant e-mails saying that we don't know what we're talking about because "don't you know that electrons are negative?!"

Even among those who understand that there is an issue between electron flow and conventional current there are misunderstandings.

A common one is that conventional current is a result of a real excess of positive charge, rather like the holes in a p-type semiconductor.

We hope that our explanation of conventional current helps non-specialists with their own understanding of this confusing area of physics.

## Conventional current has no opinion

Conventional current is confusing but it doesn't try and tell us what is 'really' happening in circuits.  Conventional current doesn't say that positives or negatives are really moving.  It just says that if real positive charges are flowing then that's great.  If it's really negatives that are flowing we simply replace them with imaginary positives flowing in the opposite direction.

By using conventional current all the time we always make sure that energy is dealt with in a consistent way.  If we use electron flow then energy cannot be dealt with in a consistent way.

back to Lesson 3: Atoms and Charge