Electricity and magnet playwiths
The main point to notice is that the top nozzle system is a metal conductor which is earthed. Statistically, the drops that fall from the nozzles will sometimes be charged. Once the first charged drop has fallen, everything else follows from that. The other key point to note is that the water jets must break up into droplets as they pass through cans A and B.
Suppose the first drop through can B is positive: that means that can B takes up a negative charge as electrons are attracted from can D. This charge repels electrons in the water, so that the droplets falling through B are more likely to carry a positive charge, passing this to the metal funnel below, in can C, and giving a positive charge to can C.
Some of this positive charge can now flow to can A, increasing the charge separation in the water flowing through the metal nozzle, so that more negative water passes through A, transferring its charge to can D, and so to can B, and so on.
Why the hoop is attracted
The main thing to watch out for is that you are not just seeing the effects of air currents. The hoop is very light, and this can happen. Try taping the magnet to a dowel that passes right through the hoop.
How the Leyden jar works
The classic Leyden jar of the physics text is a glass jar with layers of tin foil inside and out. Ideally, the outer layer is "earthed", so it will help if you sit your jar on a metal surface. The classic Leyden jar also has a piece of metal with a ball on the end, sticking up out of the centre: this makes it easier to charge the jar and to discharge it. In this case, you will be charging the jar by contact with an electrophorus , but it is probably better to keep the whole system insulated, and to charge it by induction.
And how do you charge it by induction? Bring a charged rod or electrophorus close to (but not in contact with) some part of the inner surface, then earth the outer surface, let go, and remove the charge source.
How to use the electrophorus
When you touch the aluminium, electrons flow to or from the aluminium, so the top now has no charge. When your hand is taken away, the charge from the lower half spreads out all over the aluminium, and the electrophorus has an induced charge which is opposite to the charge on the rubber mat.
The principle of the electrophorus is that charge can move through a conductor like aluminium, but it cannot move through an insulator like the rubber mat.
An old "78" record works well here, while vinyl LP records can also be used
Why does the compass needle twitch?
No compass? Look at the next mini-experiment!
How the compass works