# Homework Help: Calculating thickness

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1. Oct 18, 2014

### laramman2

1. The problem statement, all variables and given/known data
Is there any way we can measure the thickness of an exposed PTFE membrane air sampling filter? An unexposed filter (from the filter datasheet) has a thickness of 40μm. We have 5 ambient air exposed filters with the following mass concentrations: 1μg/m3 (filter 1), 20.1 μg/m3 (filter 2), 40.6 μg/m3 (filter 3) , 60.1 μg/m3 (filter 4) , and 66.1 μg/m3 (filter 5) . Also, for each filter, we performed a procedure where we transmit a 1460 lux constant light source through the filter and the reduced light intensity was captured by a light sensor. The data for that procedure are as follows:

CONTROL - 1460 LUX
FILTER 1 - 418 LUX
FILTER 2 - 375 LUX
FILTER 3 - 295 LUX
FILTER 4 - 185 LUX
FILTER 5 - 130 LUX

Btw, this is for our research. We try to determine the attenuation coefficient of each filter.

Thank you very much!

2. Relevant equations

I1d12 = I2d22

3. The attempt at a solution
Does the above equation possible to use?

Last edited: Oct 18, 2014
2. Oct 18, 2014

### Quantum Braket

Lots of questions about this one. Are the membranes saturated? Are you assuming linear scaling of light transmittance to thickness? Are the filters the same length and width in dimension? How does light attenuation scale with thickness of unsaturated membranes? How does light transmission vary in saturated vs unsaturated samples? Is the light absorbed differently for saturated vs unsaturated at that particular wavelength? Is it a single wavelength source?
What sources of errors are in your measurements?

Finally, this section is for homework problems. If this is for research then the Faq states this is not the place to put this question.