If the current flow into the load at Vout is small compared to the total current flow, then voltage at Vout is just the current times the resistance of V2.If that load is an analog input, very very little current flows, so the load is effectively 0 ohm, and Vout will equal Vin*Z2/(Z1+Z2) as described above.
Electricity needs a loop because the electrons need to go somewhere after giving up their energy.
You're not include enough in your "water" analogy. Say on your roof is a water tank that collects rainwater. The water in there has a certain amount of potential energy, because it is "up high." You can turn on a spigot and run water through your set of pipes, possibly doing some work using that potential energy. In the process the water loses the energy, and spews out the end of the pipe, somewhat lower down than it started.But that's not the actual end of the circuit! The water goes down the drain and flows to the bay. Then the sun evaporates the water (adding energy), and eventually it rains, refilling your water tank. So the water has gone around a full circuit as well. See "water cycle" in any "Earth Science" book.The sun evaporating the water and adding energy is like a solar cell adding energy to electrons in the circuit.The water tank is like a capacitor (or rechargeable battery), storing that energy so that you can use it.The water spewing out the end of your pipe is a "low resistance" path back to "ground" (perhaps it even spills on the ground.)You can make electrical circuits where electrons "spew out" the end of a wire into space (fundamental to the operation of vacuum tubes, and responsible (?) for those lovely arcs that come off of Tesla coils, for instance), but while water finds the open end of a pipe leading to air to be "low resistance", electrons coming to the end of the wire behave differently and find it hard to "jump off." A bit like holding the end of your water pipe against a block of wood, and still expecting the water to come out because "wood is made up of molecules, just like air" (a block of metal in the path will stop the flow of water, but not the flow of electrons. An airspace will stop the electrons, but not the water...)
Hmm. Some of the explanations went over my head but this seems to make sense: Electricity needs a loop because the electrons need to go somewhere after giving up their energy.Just your water pipe idea, where a pump returns the water to the top flow down again, the electrons return to a battery, say, to be re-charged flow again.So the electrons aren't exiting the system, they're just all losing their charge and returning back to Ground to get recharged and go for round 2.
Most of my analog inputs are 50 ohms.
Electrons prefer to be attached to atoms.