Probes for all purposes

31st May 1996 at 01:00
What is the connection between a hot cup of coffee and T=ABt+C?

Well, to cut a long syllabus short, it's that the equation describes the way in which cups of coffee, in staffrooms everywhere, cool. If you could only make "C" small enough, your coffee would cool faster, you could drink it before the pips go. It's maffs, innit?

You could just accept that as a fact. But if you're studying maths or science you really ought to get yourself a coffee and see for yourself.

And to make that possible, there's new equipment from the United States which lets you take the necessary measurements and then analyse them in detail.

The CBL (Calculator-based Laboratory) is a hand-sized unit into which you can plug sensors. Link the temperature sensor supplied, press a button or two and then read the temperature on a liquid-crystal screen.

There's a light probe and a voltage probe and, when you plug these in, they are automatically calibrated so you can start taking readings straight away.

You might test the voltage in a circuit as you would have done with a meter or data logger. And, as you might expect, there are other sensors - a force sensor, a pH sensor, a sound sensor. A really useful sensor is an ultrasonic motion detector which lets you measure how high a ball bounces or how things accelerate.

If you plug the CBL into the graphics calculator, you can see your measurements on a graph against time. To get that, you type in a program or alternatively use your desktop computer to send a ready-made program, which you can get from Texas Instruments, to the calculator. You can also connect two calculators and zap the program from one to the other.

What's left is a huge potential for data analysis. You now have the results in an unusually capable and portable calculator.

Take the cooling curve for a cup of coffee: the calculator will let you adjust the axes, subtract room temperature (that was "C" in the equation, by the way) from the readings, and try to fit the equation above to the graph.

If it fits, you can start to make predictions about other cooling situations.

* Calculator-based Laboratory with Temperature, Light and Voltage Probes Pounds 199 plus VAT, Texas Instruments * TI-82 Graphics Calculator Pounds 54.24 plus VAT * TI-graph link for PC or Macintosh Pounds 29.99 plus VAT Texas Instruments, Kempton Point, 68 Staines Road West, Sunbury-on-Thames, Middlesex TW16 7AX. Tel: 01784 212739

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