Subject: Re: Electrons

From: [email-masked] (Charles Moore)
Date: 15 Feb 1995 19:59:12 GMT

Amcan Inc. ([email-masked]) wrote:
:  
: A friend of mine and I both work as lighting technicians in the movie
: business. In our quest to better understand electricity we have formulated
: a question. 
:  
: To illustrate this question we give you two situations: 
:  
: Situation #1.   A 12 volt battery supplies a 20 watt bulb (rated for 12
: volts) with 1.66 amps. 
:  
: Situation #2.  A 6 volt battery supplies a 20 watt bulb (rated for 6 volts)
: with 3.33 amps. 
:  
: In the first situation the number of electrons passing throught the wire
: is half that in the second situation. What is different about the electrons
: in the first situation such that less of them can do more work? 
:  

As electrons travel through the filament of a bulb they will scatter off of
(collide with) lattice imperfections and phonons, giving up energy to the 
filament each time.  This is how the electrons heat the filament.

The filament in the first situation will be either thinner, or longer than
in the second situation.  If the filament is thinner, the electrons must go
faster to carry a given current, and will give up more energy each time 
they scatter.  If the filament is longer, the electron will have scatter
more times and hence give up more energy.  Most likely, the filament in the
second case is enough thicker so that the electrons travel at the same speed
in each situation but the filament in situation 1 will be twice as long as in
situation 2, so half the current will do the same heating.

: -- 
: Piotr Jagninski 
: (212) 260-3191 
: [email-masked] 

              charles moore hpltbr.fc.hp.com

---

From: [email-masked] (Charles Moore)
Date: 15 Feb 1995 19:59:12 GMT

: -- 
: Piotr Jagninski 
: (212) 260-3191 
: [email-masked]