Re: [Phys-l] Hewitt's three answers

["William Maddox" <maddox@physics.auburn.edu>]

From: WC Maddox

The day before I read about this in Physics Teacher I constructed a circuit
for another purpose which detected this variation in brightness of
fluorescent and incandescent lights. It use a solar cell and a National
Instruments DAQ. The voltage variation was displayed on a LabVIEW
simulation of a voltage meter.

Using the overhead fluorescent lights the voltage varied between 0.215  and
0.235 volts with peaks appearing with a frequency of 120 HZ.
Using a 25 W incandescent bulb the voltage varied between 0.265 and 0.285
volts with frequency of 120 Hz.

End Message   

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu
[mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of chuck
britton
Sent: Wednesday, March 28, 2012 8:31 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] Hewitt's three answers

Many physics professors are surprised when they see the 120 Hz 'flicker' of
an incandescent bulb displayed with a CBL or such.
.
At 4:44 PM -0400 3/28/12, Ludwik Kowalski wrote:
> Look at Hewitt's  "Flash Frequency" question (page 202 in the April 
> 2012, issue ofThe Physics Teacher). In my opinion all three answers, in 
> this multiple choice test are incorrect, in my opinion. My answer would 
> be 0 flashes.
>
> Yes, there are 120 current maxima in each second. But the light 
> intensity, in the case of an incandescent light bulb, is practically 
> constant due to "thermal inertia." Do you agree?
>
>
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