Re: Using mobile phone as an internet radio

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#22

From: Jasen Betts
Date: Sat, 06 Oct 2012 23:31

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On 2012-10-05, Roderick Stewart <rjfs@escapetime.removethisbit.myzen.co.uk> wrote:
> In article <de99517e-e5e1-4f9d-91e0-
> 412ab3171a05@o8g2000yqm.googlegroups.com>, George Herold wrote:
>> And thats it.  Repeated on and off means that the thin region has a
>> higher average temperature than the thick part of the filament.  It
>> evaporates faster and fails sooner.
>
> Won't a thin region of a lamp filament have a higher temperature than 
> the rest of it all the time, not just when the lamp is turning on?

It will, but due to the thermal coefficient of resistance of tungsten
(most other metals are similar) the heating will be even greater when the 
filament heats from cold. The hot spot gains resistance faster, so it 
drops a greater voltage while the rest of the filament is still cold.

disclaimer: figures made up to illustrate the point 

assume a constant-voltage supply  compute the power disipated by he
thin spot (middle resistor) in each case

 cold  ----[100]---[1]---[100]---

 hot   ----[1000]-[12]-[1000]----

 during warm-up thin spot warms up fastest.

 start  ---[200]---[3]---[200]--- 

yeah, it would be a good project for the mythbusters, I'd love to see
a slow motion film of an incandescent lamp failing at turn-on.
but could they affor do dedicate their fast camera for long enough.

-- 
⚂⚃ 100% natural

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From: Jasen Betts <jasen@xnet.co.nz>
Newsgroups: uk.tech.digital-tv,24hoursupport.helpdesk,uk.telecom.mobile,sci.electronics.basics,sci.electronics.repair
Subject: Re: Using mobile phone as an internet radio
Date: 6 Oct 2012 23:31:51 GMT
Organization: Dis (not Dat) Organisation
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 <de99517e-e5e1-4f9d-91e0-412ab3171a05@o8g2000yqm.googlegroups.com>
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