Ok, here's my problem. I am doing A-level physics, part of which is to plan out an experiment, something I'm now in the process of doing. The experiment is to measure how temperature affects the breakdown voltage of a zenner diode, in the temperature range of -70 to 150 degrees. I've got everything covered apart from the -70 degrees temperature point. I can use dry ice to get to a temperature of -78.2 degrees, but it needs to be -70, and I cannot find a medium to cool to -78 with dry ice and then warm up to -70 degrees. I considered gel packs, but those don't go cold enough, typicaly freezing and bursting before they reach that point. Has anybody got any ideas on what I can use? Any help would be greatly appreciated
