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 18th 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 viva introduced 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, and most of the time voltage 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.