It was a case of standing room only for the fourth Café Sci event of the year, hosted by Dr Peter Ford MBE, who kindly visited us from the University of Bath. Dr Ford performed a series of fascinating experiments involving liquid nitrogen to over 200 students and teachers.
He started off the event by demonstrating the extremely volatile nature of liquid nitrogen at room temperature by pouring it over the hall floor for it to instantly boil before our eyes. This was followed by a series of experiments explaining the relationship between the volume of a gas/liquid and its temperature. A balloon full of air was placed in the liquid nitrogen, and cooled to such a low temperature (-196 degrees) that the oxygen condensed to a liquid and the balloon shrunk. After taking it out of the liquid nitrogen, the oxygen boiled instantly and the balloon re-inflated (and exploded on a couple of occasions!).
Dr Ford then moved on to discuss the effects of low temperatures on electrical circuits and electromagnets, by dipping a battery in liquid nitrogen, which effectively slowed down the chemical reaction inside the battery so it no longer worked as well (and when taken out it warmed up and worked as good as new). He also demonstrated the “jumping ring” experiment, which consists of a large electromagnet which, when plugged into the mains, creates a massive force of repulsion which causes the attached magnetic ring to fly up into the air. When the ring was placed in liquid nitrogen, it cooled down and provided much less resistance, causing the ring to fly 4 times the height (and conveniently land in the liquid nitrogen bath, to a round of applause).
The grand finale was in the form of a “liquid nitrogen monster” which consisted of a bucket of water with some washing up liquid, into which a small amount of liquid nitrogen was poured – the liquid nitrogen boiled and blew up the bubbles creating an enormous explosion of foam.
