When you were studying GCSE physics you may have been introduced to the concept of formula triangles, such as those shown in Figure 1. I confess to having encouraged students to use them myself on occasion, although I don’t really like them. The triangle in Figure 1a — which relates to the resistance equation associated with Ohm’s Law — Ican just about cope with. Figure 1b, on the other hand — which you are supposed to remember as ‘Ivy Watts’ — is a complete disaster in terms of physics. Let me explain.
‘Ivy’, in this statement, means I multiplied by V, and these symbols refer to the physical quantities of current and potential difference respectively. ‘Watts’ refers to the unit in which the answer is measured, and so this so-called equation manages to mix both quantities and units together and pretend they equal one another. This is, of course, impossible.
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