Click Spritz to puff oil drops into the chamber
from the atomiser. Most will rise or fall — but a few will
balance and hang motionless. It often takes several spritzes
to collect enough stable drops.
You can adjust the plate voltage V.
Changing it shifts which drops happen to balance: make sure
you record the voltage you used alongside each measurement.
Click any drop (moving or still) to examine it under the
microscope. Read its radius from the scale.
For a stationary drop the electric force balances
gravity: qE = mg. Use the constants
above together with your measured radius to calculate the
drop's charge q. Collect a handful
of drops in a spreadsheet and look carefully at the numbers
you get.
No drag or buoyancy is modelled. In reality a drop reaches
terminal velocity almost immediately, so a "floating" drop
really is in true force balance.