[Humairaa Patel]

Humairaa Patel asked the Naked Scientists:
   
What is an electric circuit?

What do you think?

[Geezer]

That's a bit like asking "How long is a piece of string?"

You'll find some examples of electrical circuits here

http://www.zephyrus.co.uk/circuits1.html

[chris]

I think what he's asking is, what's constitutes a circuit in functional terms; in other words, what's actually happening when the components of a "circuit" are connected together?

C

[Geezer]

Ah! Right!

Well, that would perhaps be a conduction path (a wire, or anything that can conduct electricity) connected across some source of electric potential (that might be a battery, a capacitor, a generator, or many other things).

The source of electric potential will cause electrons to migrate through the conduction path. The electron flow constitutes an electric current, and the magnitude of the current is a measure of the number of electrons flowing in the conduction path. (Current is generally measured in Amperes)

The electrons actually flow through the conduction path from the negative side of the potential source to the positive side. That's because electrons have negative potential, but at the time when the convention for current flow was established, the potential of electrons was unknown.

[syhprum]

The current is not always the flow of electrons in a liquid it can be a flow of ions or in a doped semi conductor it can be a flow of 'holes' (areas that are deficient in electrons) that behave as though they are positive particles.
But in the simple case of a metallic conductor it is a flow of Electrons that takes place. 

[Geezer]

Good point Syphrum. Electron flow in thermionic devices like CRTs and valves/tubes might be another form of current flow without a conductor.