A teaching clock for teaching the concept of elapsed time includes a clock face having a minute hand and an hour hand pivotally mounted to the clock face and an elapsed time indicator having an hour hand and a minute hand that move synchronously with the movement of the clock hands. The filter support includes at least two opposing pleated walls, and at least two opposing sidewalls connected at a first end of the filter support to define a fluid flow aperture. One of a source and a drain of the first transistor is electrically connected to a first wiring, and the other thereof is electrically connected to a second wiring.