|MadSci Network: Chemistry|
Thanks for your question, Professor. The strip changing color is temperature- sensitive liquid crystal. At a threshold temperature, the strip changes color, either exposing a length of green or exposing the word, "good." The trick is a conductive strip cut into a taper under the liquid crystal. The current is constant in the strip, but the current density where the strip narrows is higher, so the strip gets hotter there. Thus, a temperature distribution is caused along the strip and the length that changes color indicates battery ability to supply current. A weak cell cannot keep the whole strip hot enough for the liquid crystal to exhibit its color change. I thank Duracell for sending my colleague some strip samples at his request. Larry Skarin
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