Dear Mr/Ms Junior Cert Syllabus writer,

The time has come to question why the concept of voltage is still on the Junior Cert syllabus.

It is by far the most difficult concept for students (and indeed teachers) to grasp.

Consider a relevant extract from the Junior Cert Science syllabus

Set up a simple electric circuit, use appropriate instruments to measure current, potential difference (voltage) and resistance, and establish the relationship between them

Let’s take a look at potential difference (commonly referred to as ‘voltage’):

*The following extract has been taken from the minutes of a History of Science meeting, in 2002.*

John Roche, of Linacre College, Oxford, opened the session after tea, speaking on the concept of voltage. He began by claiming that

almost every concept in electricity and electromagnetism is ambiguous, and the concept of voltage is one of the most incoherent. Its evolution is difficult to follow.Abbé Nollet, in the 18

^{th}century, distinguished quantity and degree of electrification. Others made similar distinctions between quantity and intensity or tension or pressure – what we would call voltage.Roche showed how the term “voltage” had come to be used nowadays in three different ways; for electromotive force, potential difference and (absolute) potential.

Volta defined electrical tension as the endeavour of the electrical fluid to escape from a body.

Volta’s tension was more akin to a force, unlike the modern definition of electromotive force, which is a misnomer, being defined in terms of energy.Ohm carried Volta’s concept to closed circuits with the idea that voltage was proportional to the difference in tension between the ends of a conductor. For Ohm, it was the gradient of electrical tension that drove the current.

Poisson introduced an entirely different concept, of charge divided by distance to a point, which Green called the potential. This was an analytical device only, arising from an analogy with Laplace’s gravitational potential function.

Kirchhoff reconciled Volta’s tension with Poisson’s potential function through the concept of energy or

vis vivaintroduced by Helmholtz. From Kirchhoff, current is driven by the electric field in a conductor and voltage is related to the energy supplied, but physicists and electrical engineers do not usually think of them in this way.

All the earlier interpretations remain current, but with different weights, andmost of the timevoltage is seen as a driving energy.

IOP History of Physics Group Newsletter, Spring 2000, page 65

So what exactly should we be telling our students about potential difference? How many (non-physicist) science teachers can define or explain potential difference? Maybe most can, but if so I would be very pleasantly surprised.

Would it hurt anyone if we replaced the syllabus extract above with something more simple, like the following?

Set up a simple electric circuit using appropriate instruments to light a number of bulbs in series.

Understand that for current to flow a power supply and a complete circuit are required.

The other aspects of the syllabus on electricity could remain as they are, but no Ohm’s Law, no experiment to verify Ohm’s Law, no mathematical problems based on Ohm’s Law, and no more mention of potential difference.

Are you kidding? I agree that there are many teachers who find the concept of voltage difficult: as there are many who find gravitation, fields, pressure, circular motion, rotational inertia and weight, difficult.

What these teachers should do is understand their subject.

“If you can’t explain it simply, you don’t understand it well enough” – Einstein

… and if you don’t understand it well enough, you have no business trying to teach it.

… and in a slightly more constructive tone:

Children, even very young children, understand energy. I tend to describe the voltage in terms of energy. It is, after all, what it is.

Batteries store energy. Connect them to a circuit and the charges run around to the end of the circuit. A bulb/motor/buzzer takes energy from the charges (so they have to do work going through one) and turn it into light/movement/sound energy. Before and after a bulb/motor/buzzer there is difference in energy, in the same way as there’s a difference across a battery. See, look at the meter…

and so on.

Voltage is energy. Everyone has a concept of energy.

Note that this is the Junior Cert Science syllabus – roughly equivalent to GCSE, most students do not go on to study phyiscs at a later level and most of the teachers are not Physics teachers.

Whether these should understand the concept or not is an argument for another day – the fact is that for not they do not. I am pretty sure that I am doing an injustice to some of the Chemistry and Biology topics that I teach at Junior Cert level and I’m not even aware of it.

In relation to the analogy with energy, yes you can (indeed must) teach potential difference from an energy perspective, but I’m not sure that understanding energy is straightforward either.

There is a lot more to say but that’s why I made it post #1. I figured if I put the arguments into different posts they would have a greater chance of being noticed.

My main point is, there comes a stage when beating heads against walls is not working, the current situation is counter-productive in that in the main it only causes confusion, so why fight it?

Cheers,

Thanks for the explanation. We have a similar situation up here in Scotland with our new curriculum, which, in my humble opinion*, requires subject specialists to teach specialist subjects: I fully understand your comment about Chem and Bio: I am certain that I have failed to give the best (or even right) explanations of aspects of these subjects because I don’t have the depth of understanding required to teach it well.

Nick

* http://mrhood.net/tite/2009/09/06/curriculum-for-excellence-the-end-of-integrated-science/