This week we tried setting up a lab to measure the intensity of light
transmitted through 2 polaroids as a function of theta - Malus' Law - using
the Pasco light detector connected to a 700 interface. The light source was
a 12V halogen bulb, and the detector was shielded in a tube of black paper
with the two polaroids at one end. The probe was calibrated in Pasco Science
Workshop with the max voltage about 5V assigned 100% and the min voltage
about 2 volts assigned zero.
The setup seemed to work, but a funny thing appeared, for which I have no
explanation. With the polaroids at some arbitrary position, and everything
left untouched, the reading from the probe oscillates with a period of about
15s and an amplitude about 5%. This goes on consistently for hours. I assume
it has something to do with the probe/interface since this is the black box
part of the setup. (First we were using a laser and I thought it was the
laser polarization changing as the tube warmed up but exactly the same thing
appears with and incancescent source).
Does anyone have an explanation?
Mark.
Mark Sylvester
United World College of the Adriatic
34013 Duino TS
Italy.
msylvest@spin.it
tel: +39 49 3739 255