The intensity of light changes with distance as an inverse-square law.
Watch Video:
Theory:
The intensity of light drops off as a function of distance from the source as an inverse-square law. To whit:
I = Io/d2
where I is the intensity, Io is the intensity at the source, and d is th distance from the source to the observer. This comes straight from Maxwell's equations for electromagnetism.
Apparatus:
- PocketLab Voyager
- portable smart device (phone or tablet)
- light source
Procedure:
- Set up your light source. Ideally, it should be the dominant light source in the room. Turn off as much outside light as possible.
- Setup the PocketLab Voyager to simultaneously measure distance (rangefinder) and light intensity.
- While taking data, physically move the PLVoyager towards and away from the source. The light detector and the rangefinder both measure from the orange front face of the enclosure.
- Once you have repeated the motion several times, stop the data taking and save the data.
- Plot the light intensity versus distance and see the 1/d2 dependence,
