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Re: brightness vrs. power



On Thu, 4 May 2000, brian whatcott wrote:

At 15:16 5/4/00 -0400, Robert wrote:

Unless I'm mistaken (if I am, I'm sure someone will correct me)...
/snip/
you are comparing a single light bulb...

---------------X-------------

with the following series-parallel configuration...

/-----X------X-----\
----- -------
\-----X------X-----/

[snip]

That's right. If the power dissipated is greater, the beginning
student should expect the four lights to be brighter. They aren't.

Actually, I thought beginning students would guess (assuming constant
resistance) that the total current in each case would be the same and so
each light bulb in the second circuit would be half as bright as the lone
light bulb in the first circuit.

If Robert believes that beginners expect twice the illumination from the
same electrical power input to a series parallel arrangement of four bulbs
as to a single bulb, does he give them too little credit, or do we give
him too much? :-)

Hmmm...I hope this is a false dilemma... :)

In any event, I asked because I was unclear on the set-up and thought
others might be also. In case anyone shared my confusion, my mistake was
that I interpreted Leigh's "four lights to be brighter" to mean that "each
light will be brighter". Now that I recognize my mistake, it makes sense
and I agree that beginning students (who assume R is constant) will guess
that the four lights *together *will be brighter than the one alone (but
that each individual light will be dimmer than the one alone). Thank you.

----------------------------------------------------------
| Robert Cohen Department of Physics |
| East Stroudsburg University |
| bbq@esu.edu East Stroudsburg, PA 18301 |
| http://www.esu.edu/~bbq/ (570) 422-3428 |
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