Doesn't Alternating current cause fatigue?

[rohanprabhu]

Take the case of a lamp bulb. When applied an Alternating current across it.. it basically goes on and off 50 times in a second [in India atleast.. we get 50Hz]. Now, it means that the filament gets hold and cold continuously. From wikipedia:

fatigue is the progressive and localised structural damage that occurs when a material is subjected to cyclic loading.

so.. is alternating current more damaging for appliances as compared to DC? Almost all electronic devices convert AC to DC.. so they are out of the question... I'm thinking about the rest of the simple devices.. like light bulbs and stuff.

 

[Doc Al]

Do think that the temperature of the filament has time to change much during each current cycle?

 

[rohanprabhu]

Do think that the temperature of the filament has time to change much during each current cycle?

so.. you basically mean to say that the temperature of the filament remains more or less constant?

 

[Doc Al]

so.. you basically mean to say that the temperature of the filament remains more or less constant?

I haven't studied the matter, but that's what I would expect. (Where are all the light bulb engineers when you need them?) I would expect most thermal fatigue to occur when you first turn on the bulb.

 

[Danger]

I would expect most thermal fatigue to occur when you first turn on the bulb.

That's what I was taught, and empirical evidence seems to support it. I have absolutely never in my life seen a light bulb blow out except when first turned on. That's the same reason that I never shut my computer off; supposedly the thermal expansion/contraction is the main failure point for the internal circuitry. (The HD and screen go to sleep on their own, so I'm not sure that there's any benefit from their perspective.)

 

[TVP45]

Well, think about common flicker. We all see it in flourescent bulbs, yet we don't see it in incandescent bulbs.