A team of physicists zapped small cubes of glass in a furnace with an electric voltage about what you'd get from an outlet in your home.电足够加热玻璃，which was already quite warm from the ambient heat of the furnace.But it shouldn't have beenenough currentto boil the glass.Glass doesn't boil until it reachestemperatures thousands of degreesabove what the current should have produced.And yet,in their oven,当电流流动并产生电场时，the physicists saw a thin "wisp of vapor" rising from the glass sample.
Here's the deal: When an electric current passes through a uni澳门金莎网上游戏form material,it's supposed to heat the whole material evenly.Scientists call this Joule's first law,after the British chemist James Prescott Joule,who discovered it in the early 1840s.这是一个物质事实，根植于conservation of energy,one of the most fundamental rules that govern our universe.And we see it at work every day;light-bulb filaments wouldn't have their nice,即使工作时没有焦耳定律也会发光。
但这股水流似乎触犯了法律。Not only did vapor rise from some parts of the glass,but a hotspot (visible on an infrared camera) danced giddily across its surface.Again and again in their experiments,hotspots appeared.
"This glass is uni澳门金莎网上游戏form on the most minute level," Himanshu Jain,a materials scientist at Lehigh University in Bethlehem,Pennsylvania,and co-author of a paper describing the phenomenon published Feb.26英寸自然科学报告杂志.
玻璃是绝缘体，不能很好地传导电流；不管多小，it is expected to turn most of that current into heat.对于焦耳第一定律的传统思考会预测电流会均匀地加热玻璃，causing it to slowly melt and de澳门金莎网上游戏form,杰恩告诉《现场科学》澳门金沙网上游戏。And under most circumstances,事情就是这样。
"We looked at the softening of hot glass under an electric field," Jain said,"and that's the thing that nobody had done before."
That uneven heating,it turned out,在玻璃阳极附近倾倒能量，the entry point for the current.So the glasswas melting在那里蒸发，即使它在其他地方保持稳定。The temperatures in the hotspots were much hotter than the rest of the glass.At one point,在不到30秒内加热2500华氏度（1400摄氏度）的单个玻璃区域。
So was Joule's law broken?是和否，Jain said;macroscopically thinking,看来是这样。Microscopically speaking,the answer would be "no" — it just didn't apply to the glass as a whole anymore.
根据焦耳第一定律，均匀的电场澳门金莎网上游戏应使材料受热均匀。But at high temperatures,the electric field doesn't only heat the glass — it changes its chemical makeup.
Electric fields move through glass when positively charged ions (原子去掉带负电荷的电子）被击出位置，带着电荷穿过玻璃，Jain said.最轻的离子最先移动，carrying the electrical current.
The glass in this setup was made ofoxygen,钠和硅.Sodium,the loosely-bonded lightweight ion,did most of the energy transport.Once enough sodium shifted,it changed the chemical composition of the glass near the anode.And once the chemistry changed,the glass was more like two different materials,焦耳定律不再统一适用。澳门金莎网上游戏A hotspot 澳门金莎网上游戏formed.
No one had noticed the effect before,杰恩说，likely because it doesn't kick in until the glass is already pretty hot.The material in this experiment didn't develop hotspots until the furnace reached about 600 F (316 C).玻璃不太热，but it's much hotter than the conditions under which most electrical machines using glass and electricity work.
Editor's note: This article was updated to indicate that Joule's law was broken from one perspective but not another,as well as to fix the chemical makeup of the glass setup.
Originally published on澳门金沙网上游戏.