Time measurements with water droplets

Project Details

Measuring rate of creation of water droplets using a laser beam + Phototransistor combo along with the various measurement tools of the SEELablet.

From a pedagogical perspective , this experiment can be used as an approximate analogy to explain the rate of discharge of a capacitor connected across a constant load.


Water droplets from a burette intercepting a laser beam.

The corresponding intensity fluctuation is recorded by a phototransistor connected to the SEN input.

The analog data logger utility is used to first ensure that the intensity fluctuations stay within well defined thresholds in order to switch to the digital time measurement utilities.

In this case , the presence of the uninterrupted laser beam ensures voltage levels below 1V , and presence of an interrupting water droplet causes the levels to rise above 3V

We then switch to the logic analyzer utility , and configure it to record the rising edges from a comparator in the SEELablet that is internally connected to the SEN input we monitored via the analog logger.

Clean timestamps with uS accuracy shows the drop rate as a function of water pressure (Level of water in the beaker )

The limiting factor in the measurement setup is the phototransistor that has a response frequency of around 2KHz , but that is more than enough for this experiment where drops fall at a rate less than ten per second.

  • This work is being pursued by students at Farook College, Calicut, And we hope to see more detailed documentation soon!