Flashing bulbs and smoke rings

While asking young people why the sky is blue (OPN, August 1991), I found that several of them wanted to know why a light bulb works. This is hardly a sophisticated optical phenomenon, yet it can be a mystery to youngsters who may not be aware of filaments or electrical currents. More importantly, the question can provoke a nice set of experiments* that are both entertaining and enlightening (if you'll pardon the pun). For these experiments, you will need the following supplies: 1 flashlight, 2 or more flashlight bulbs, 2-3 D cell batteries, 19V battery, 1 candle, stranded #22 insulated wire, masking tape, and needlenose pliers. In this sequence of experiments, we show first how a bulb works, then demonstrate the simple principles behind why it works, and finally demonstrate these principles directly with a bulb.

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