12 May
2010
12 May
'10
10:59 a.m.
On 11 May 2010 at 21:52, Tony Duell wrote:
Sure. i never actually saw the original post... It would be interesting
to measure the votlages across the various bulbs in the OP's circuit.
Since they are in series, they are both passing
the same current.
Therefore the power disipated is porportional to the resistance. A 40W
bulb will have a higher resistance than a 100W bulb, so, making
reasonable assumptions about the bulbs, the 40W one will be brighter.
Yes, I was sort of hinting at a possible solution to the original problem--in fact, the resistance difference becomes
much larger as
the 40W lamp begins to glow. If you put the series-connected lamps
on a variac and slowly inch the voltage up, it's surprising how the
positive temperature coefficient of resistance starts kicking in.
That is something I am going to have to try (having never done it).
But most people will, without thinking, say "Oh, a 100W bulb is
brighter than a 40W, so the answer is obvious." And wrong.
These are the same people that think you _have_ to draw 13A from a 13A
mains socket, i guess ;-)
[A buyl disipating 100W is likely to be righter than one disipating 40W.
But in this circuit, the buls are not disipating their rated powers]
But then we learn more when something doesn't work
the way it's
"supposed to", than when it does, don't we? That's one issue I have
Of course. I can't rememebr who said it, but there's a quote something
like "The words that come before the greatest progresses in science are
not "Eureka" but "Hey, that's curious"'
with a lot of secondary-school laboratory courses.
You do the
experiment, can pretty much guess from the course material what's
going to happen and it does. Time for lunch.
One thing that I learnt very early on (from my parents, not at school, I
hasten to add) is that if something does not do wht you expect, you stop
and investigate. Most of the time it will be because you've done
something silly. Just occasionally it's because there's something
interesting going on.
Back when I was taking a course in numerical methods, I had a teacher
who'd assign seemingly easy programs. You had a week to code it up;
just about any text would have the method documented. He'd post the
data set the day before the assignment was due.
Of course, after about the first two assignments, you learned that
his data were going to be pathological and destined to break any "out
of the book" method. In a previous life, he'd worked for NASA and I
suspect, learned things the hard way.
That's the sort of teacher I would like...
-tony