The filament in the Edison bulb is made of very fin […]
The filament in the Edison bulb is made of very fine tungsten filament. When the normal operation of the temperature reaches 2000 ℃, although it can not reach the melting point of tungsten wire 3370 ℃, but this high temperature can make part of the tungsten surface of the atoms evaporate. Therefore, the bulb after a long time, the glass bubbles will slowly turn black, the filament will slowly become thinner, become thin no longer so uniform. Since the resistance of the conductor is related to its cross-sectional area, the electrical resistance per unit length of the fine unit is larger than that of the thicker unit, and the heating power is larger than that in the thicker place. Therefore, the finer the local temperature is higher The Uneven heat, not only will make the filament deformation, but also make the spiral filament turns of the pitch is not uniform, resulting in more uneven heat, the more the number of turns, the higher the temperature. For most conductors, the resistance and temperature, the higher the temperature, the greater the resistance.
Most people think: Edison bulb open before the filament is cold, its resistance is very small; in the light of the moment, through the filament current is very large, about 10 times the normal current when the light. Therefore, the moment of turning on the lamp, the filament heating power is much larger than normal light, which makes it possible to make the filament temperature of the compact, compact part reach or exceed the melting point of the tungsten filament, causing the filament to be melted. So the bulb with a long time, when the lights, the filament easy from the thinning, dense place burned.
But the problem is: open the moment the temperature has not risen, why the filament but easy to break? In fact, there is an important reason there: filament and lead bracket connection is not strong, resulting in a certain contact resistance, especially in the light of its consumption A substantial increase in power, coupled with the heat of the filament itself, it is easy to cause local overheating and blown filament!http://www.outedsionbulb.com/