Replace the capacitor C2 from the last experiment by a 10 μF capacitor
The LEDs light up a little shorter than what you expect from a 10 μF capacitor. And indeed, you calculate the total capacity as...
Ctotal = ( C1 * C2 ) / ( C1 + C2 ) = ( 100 μF * 10 μF ) / ( 100 μF + 10 μF ) = 9 μF
The total capacity of a series circuit is always smaller than the smallest capacity in the circuit. If you replace the capacitor C2 by the 47 nF ceramic capacitor, you get a total capacity of slightly less than 47 nF.
If you want to understand the reasons, you should have a look at the topic capacitor in physics.
But first, enough is said about the properties of capacitors. In the following experiments you see where and how capacitors are used.