MadSci Network: Chemistry

Re: How does it work, the tester included in many alkaline batteries ?

Date: Mon Dec 7 12:26:29 1998
Posted By: Lawrence Skarin, Faculty, Electrical Engineering, Monroe Community College
Area of science: Chemistry
ID: 911961977.Ch

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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