pipaxy#306
Nem gondolom ezt partalan vitának bár az tény hogy a tankönyv azon állítását nem tudom bizonyítani, mondjuk egy tankönyv bizonyítását nem is érzem igazán feladatomnak (és nem is tartom szükségesnek). De ez mindegy is, hiszen amit írtál a verebes példára azzal én is egyetértek. A kérdés csak az mennyivel él tovább a kalitkában?
Erre linket pedig találtam, ebből: Since bulbs usually burn out during the current surge that occurs when they are turned on, one would expect that eliminating the surge would save light bulbs.
In fact, such devices are available. Like the diode-based ones, they are available in a form that is built into caps that one could stick onto the tip of the base of a light bulb. These devices are "negative temperature coefficient thermistors", which are resistors having a resistance that decrease when they heat up.
When the bulb is first started, the thermistor is cool and has a moderately high resistance that limits current flowing through the bulb. The current flowing through the thermistor's resistance generates heat, and the thermistor's resistance decreases. This allows the current to increase in a fairly gradual manner, and the filament warms up in a uniform manner.
However, this extends the life of the bulbs less than one might think. If the filament has thin spots that cannot survive the current surge that occurs when the bulb is turned on, then the filament is already in very bad shape. At this time, the thin spots are significantly hotter than the thicker parts of the filament and are evaporating rather rapidly. As described earlier, this process is accelerating. If the thin spots are protected from surges, the life of the bulb would be extended by only a few percent.
Additional life extension occurs only because the thermistor keeps enough resistance to result in enough heat to keep it fairly conductive. This resistance slightly reduces power to the bulb, extending its life somewhat and making it slightly dimmer.