General question on electricity

[jerryyu]

I always have difficulty accepting the analogy between the flowing of electrons because of potential differences and water flowing downhill. The reason is shouldn't electrons begins to flow once the wire is connected to it? Why does it needs a complete circuit?

 

This is a very general question, and I hope someone could get my thinking in the right direction.

[swansont]

Air is not an "open connection" for current as it is for water. Air has a really high resistance. What happens to flow of there is a cap on the end of a hose or pipe?

[ewmon]

A battery sitting on the shelf has a very small current of electrons flowing through the air from one terminal to the other. Connecting a wire to one terminal will also cause a very small current of electrons to flow down the wire.

[jerryyu]

Sorry for the misunderstanding. What I mean is the potential differences pertaining to electricity is often compared with water falling downhill

 

What my question is, is why do you need a complete circuit to get a voltage reading on a volt meter. Shouldn't the electrons start flowing once it's connected to the terminal that the electrons is oxidized.

[swansont]

You don't need a completed circuit to get a voltage reading; you can read a battery. Unless you are talking about the voltmeter itself, and that's due to how one makes the measurement.

[TonyMcC]

I always have difficulty accepting the analogy between the flowing of electrons because of potential differences and water flowing downhill. The reason is shouldn't electrons begins to flow once the wire is connected to it? Why does it needs a complete circuit?

 

This is a very general question, and I hope someone could get my thinking in the right direction.

 

An easier water analogy to understand is to consider a closed water circuit such as a pump pushing water through (say) radiators.

The pump provides pressure to force the water around the circuit and in many ways is similar to a battery forcing electrons around an electrical circuit.

The pipework and taps on the radiators offer opposition to the water flow and can be likened to resistors in an electrical circuit.

If you completely close a tap you will stop the flow of water. In an electrical circuit you do the same by providing an extemely high resistance. This happens if you break the electrical circuit. Note this does not stop the pump producing pressure nor the battery producing voltage.

[ewmon]

why do you need a complete circuit to get a voltage reading on a volt meter. Shouldn't the electrons start flowing once it's connected to the terminal that the electrons is oxidized.

 

The waterworks analogy of voltage is water pressure, which exists and can be read without flow.

 

The waterworks analogy of electric current is water flow.