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Re: lightbulbs

Measure the actual, in-circuit voltage across each bulb, and the actual,
in-circuit current.
Division gives the actual, in-circuit resistance. VI=I^2R gives the
actual, in-circuit power (should correlate to brightness). Disregard
your measurements of cold, out-of-circuit resistances.
Please report your new results.

Bob

Bob Sciamanda
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor
----- Original Message -----
From: Yvon Jean <phys@NTL.SYMPATICO.CA>
To: <PHYS-L@lists.nau.edu>
Sent: Tuesday, November 09, 1999 5:34 PM
Subject: lightbulbs


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Here's a simple experiment I'm having trouble with. Our grade 9
science text suggests experimenting with different voltage miniature
screw ligntbulbs operated at the same voltage. The purpose is to find
the relationship between the resistance of the bulb and the illumination
produced by the bulb.

I tried 3 bulbs (1.5 V, 3.8 V, 6V) sequentially wired to the same 1.5
V drycell.
The least light is obtained with the 6 V bulb and the most light with
the 1.5 V bulb, as I would have anticipated. But here is where it gets
complicated. I would expect that the greatest the voltage rating of the
bulb, the highest would be its resistance and lowest its current.
The current and resistance values were obtained with a digital
multimeter. Here are the results:
1.5 V bulb 3.8 V bulb 6 V bulb
1.6 ohms 2.9 ohms 1 ohm
0.22 A 0.18 A 0.28 A

The results were consistant with different bulbs from the same batch,
and were triple verified. Please enlighten...

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<DIV><FONT size=2>Here's a simple experiment I'm having trouble
with.&nbsp; Our
grade 9 science text suggests experimenting with different voltage
miniature
screw ligntbulbs operated at the same voltage.&nbsp; The purpose is to
find the
relationship between the resistance of the bulb and the illumination
produced by
the bulb.</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT size=2>I tried 3 bulbs (1.5 V, 3.8 V, 6V) sequentially
wired
to&nbsp;the same 1.5 V drycell.</FONT></DIV>
<DIV><FONT size=2>The least light is obtained with the 6 V bulb and
the most
light with the 1.5 V bulb, as I would have anticipated.&nbsp; But here
is where
it gets complicated.&nbsp;I would expect that the greatest the voltage
rating of
the bulb, the highest would be its resistance and lowest its
current.</FONT></DIV>
<DIV><FONT size=2>The current and resistance values were obtained with
a digital
multimeter.&nbsp; Here are the results:</FONT></DIV>
<DIV><FONT size=2>1.5 V bulb&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; 3.8
V
bulb&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; 6 V bulb</FONT></DIV>
<DIV><FONT size=2>1.6 ohms&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; 2.9
ohms&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; 1
ohm</FONT></DIV>
<DIV><FONT size=2>0.22 A&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;
&nbsp;&nbsp;&nbsp;
0.18 A&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;
&nbsp;&nbsp;&nbsp; 0.28 A</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT size=2>The results were consistant with different bulbs
from the same
batch, and were triple verified.&nbsp; Please
enlighten...</FONT>&nbsp;</DIV></BODY></HTML>

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