The idea to use smartphone for measuring the light intensity passing trough 2 polarizers as cos² of the angle between their axes (Malus’ law) is not new. See, for example, Martín Monteiro, Cecilia Stari, Cecilia Cabeza, and Arturo C. Martí, "The Polarization of Light and Malus’ Law Using Smartphones," The Physics Teacher 55, 264 (2017); doi: 10.1119/1.4981030 . But not all telephones have a light sensor
. So, here is an experiment using the SensorTag of Texas Instruments controlled by a smartphone via Bluetooth. The corresponding phyphox program is attached here. The angle of rotation is determined from x and y components given by the SensorTag acceleration sensor. It is much easier to rotate the SensorTag than a smartphone. One polarizer film is in front of the light source and another is attached to the SensorTag.
There is a little problem of synchronization of two sensors
. It is not sufficient to use the same interval of measurements (0.8 s)...
It works very well also with a LCD screen as a polarized light source. So you need only one small polarizer covering the optical sensor of the SensorTag.
I have totally missed that the SensorTag includes a light sensor. This opens a whole new world for me iPhone user…
Could you please add a “version” attribute to the “phyphox” element: phyphox complains (in iOS?) on import.
I will try your experiment out this evening.
(12-14-2020, 12:50 PM)Jens Noritzsch Wrote: [ -> ]Could you please add a “version” attribute to the “phyphox” element: phyphox complains (in iOS?) on import.
The app on i(Pad)OS is more strict on XML compliance. The “version” attribute is mandatory so expect that leaving it out could raise errors on Android in the future, too. The attribute helps us to keep backwards compatibility if we ever need to change default behavior…
I have added the "version". Thank you for outlining its necessity. Should I indicate "1.6" or lower? Please explain me if other attributes of "phyphox" are important. Unfortunately I do no have an i-phone.
The photo of "THE DEVICE"
might be also useful. Tell me if it works now...
(12-14-2020, 05:59 PM)solid Wrote: [ -> ]The image of "THE DEVICE" might be also useful. Tell me if it works now...
Hm, I do not get it: image…? Works perfectly. We would recommend the latest version!
(12-14-2020, 06:46 PM)Jens Noritzsch Wrote: [ -> ]Hm, I do not get it: image…? Works perfectly. We would recommend the latest version!
I mean the photo of the wood support of the SensorTag with a polarizing film covering it. The support allows easily rotate the SensorTag over 360° many times.
(12-14-2020, 08:26 PM)solid Wrote: [ -> ]I mean the photo of the wood support of the SensorTag with a polarizing film covering it. The support allows easily rotate the SensorTag over 360° many times.
Very good. I would perhaps go the “traditional” way: LEGO (as soon as I get access to it)…
Is there a specific reason that you have not combined the two bluetooth blocks: you would like to connect to just one SensorTag, wouldn't you? The current experiment asks twice for a device.
There were no reason to call the bluetooth device twice. I just thought that I have to do it for two different sensors. Now I combined both SensorTag sensors in ONE bluetooth block and it still works. Thank you, Jens.
So, now this version is recommended 
.
Mikhail
Hi everybody!
Just to be able to compare the results of the Malus law measurements using the Sensor Tag as described above and only a Samsung smartphone (phyphox has access to the light sensors only on Android devices) I would like to add phyphox file for the latter.
The given experiment has two screens:
Graph [
attachment=542] showing the Malus law obtained while rotating the smartphone covered by a polarizer in front of a computer screen and Diagram [
attachment=543] showing the ratio of x and y accelerations used to determine the rotation angle.
The final result (pdf file) obtained with the smartphone shows a cutoff at low intensities unlike the result with SensorTag published earlier.