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Re: brightness vrs. power



On Fri, 5 May 2000, Robert A Cohen wrote:

On Thu, 4 May 2000, brian whatcott wrote:

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,

I think brian was alluding to an apparent error in your own reasoning:
Under the naive assumptions 1) that the resistance is independent of
current and 2) that the illumination from each bulb is proportional to the
electrical power consumed by each bulb, the students should predict that
the total illumination is the *same* in both cases.

John Mallinckrodt mailto:ajm@csupomona.edu
Cal Poly Pomona http://www.csupomona.edu/~ajm