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I have a project involving the detection of the presence of water in a cylindrical transparent plastic container (diameter=25cm)

And I cannot put any device inside, so I was thinking of using and IR LED and IR sensor so do you think this is possible ?

How can I make the difference when the container is empty (contains air) and when it has water ?

How does infrared light behave in both cases?

Also will the plastic body of the container interfere ?

Basically, if we omit the plastic(as it'll have static value), will the intensity of ir light decrease when passing through water(compared to air) ? how much percent ?

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In general, what you would need to know to completely calculate the situation through, is the wavelength-dependent absorption of your plastic and water and the characteristics of your LED (wavelength, spectral broadness, etc.). And yes, in general, most plastics have IR-absorption (which is why IR spectroscopy is used in plastic analytics). But depending on your plastic, there might still be enough coming through to detect a signal. According to an arbitrarily googled source (here), water has absorption in the IR-regime. Whether the signal difference is big enough will depend on your plastic wall thickness and the material, BUT in the end, if you can, try it - or try to obtain better data on your materials and apparatus.

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  • $\begingroup$ so, theoretically it's possible, i wanted to know that before buying components $\endgroup$ – Xsmael Jul 21 '16 at 16:59
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    $\begingroup$ I cannot guarantee you whether the difference in intensities is high enough, though, so try to find the absorption spectrum from the plastic you are using first and see how sensitive the sensor you are about to buy is ... $\endgroup$ – Sanya Jul 21 '16 at 17:01
  • $\begingroup$ so basically, if we omit the plastic(as it'll have static value), will the intensity of ir light decrease when passing through water(compared to air) ? how much percent ? $\endgroup$ – Xsmael Jul 21 '16 at 17:02
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    $\begingroup$ That depends on the IR wavelength and the unit of your diameter in the question. Once you have that, you can use the Lambert-Beer law together with absorption parameters for air and water to calculate it through. $\endgroup$ – Sanya Jul 21 '16 at 17:06
  • $\begingroup$ oh sorry for the diameter, it's 25cm (i edited my post), Ouawh! i never thought it would be that complex, i'm not a fan of physics just got that idea, but you, gave me a way to go at least, thanks a lot! $\endgroup$ – Xsmael Jul 21 '16 at 17:12

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