### Answer to sTEm–at-Work Puzzle #54: Signal Analysis for a Resistance based Temperature Sensor

The Puzzle: http://flate-mif.blogspot.com/2016/08/stemat-work-puzzle-54-signal-analysis.html

Analysis
Students have trouble visualizing the power calculation for sine wave forms. The puzzle has the typical practice of presenting the power calculation as three different AC signal forms. Ask students to find plot locations where IV equals zero and then have them pick other current/voltage value locations and think about the multiplication of those values. If they don't see it, get them to realize that between 10:01:03 AM and 10:01:05 the current and voltage value pairs are negative values. This means that the purple plot behaves like a power curve for the first 2 seconds but not during its last two seconds. Thus, the purple curve may still be a power curve but it can NOT be the power curve for this situation.

Question
Do the three plots below represent what the Technician expects to see in this constant temperature situation?