The last straw

It's now 18 years since I gave up working full time as a teacher in the local Sixth Form College (an establishment of further education for 16 - 19 year olds). I'd been finding the work more and more annoying for the simple reason that I could see it going on forever and felt that I was in a mental straight jacket. Partly this was because my one major initiative, a course that looked at the relationships between science, technology and society, had failed to recruit quite enough students that year and had therefore been cut, and partly because I was fed up with thinking about things on other people's behalf rather than my own.

The last straw, the one that broke this camel's back as it were, came when I was helping a student with his project work. In his case it was to determine the efficiency of a light bulb and the first thing that we'd decided to do was to see if we could get some idea how much heat, as opposed to light, the bulb was giving out. Because we were only dealing with low voltages there wasn't much problem with simply dunking the bulb in a beaker full of water, taking care to keep the terminals dry, and seeing how much the water heated up. If you know how much water you've got and how much its temperature has risen you can work out how much heat, at a minimum, the bulb must have produced. If you also measure the electrical energy put into the bulb ( Energy = Voltage x Current x Time ) you can get a first estimate of what proportion of the energy put into the bulb had been turned into heat.

So far so good, but then came the insightful bit. Whilst we had some idea of how much heat the bulb was producing we still didn't know how much energy was being carried away by the light. Now evidence suggests that I do my best thinking not when trapped behind a desk but when either walking or cycling, so its most likely that my brief moment of revelation came when cycling to or from the college. Suppose, I thought, you put a small drop of ink in the water. All of a sudden you can't see the bulb even though, presumably, its still producing light. This means that the light energy must have been absorbed and would reveal itself as an additional rise in the temperature of the water. Brilliant...or so I thought.

When I next saw the student I gently talked him through this idea, in such a way that he could almost have thought that he'd thought of it for himself, and then left him to get on with it. 

But, when the time came to present the work it turned out that he simply hadn't been bothered to conduct the extra brief experiment and had completely ignored my brilliant suggestion.

That was it, enough of thinking about things for other people just so that they could be ignored. The final straw may not have been very big but it was big enough.