What are the two basic types of electric circuits?

Answer 1

There are many different types of circuits, but, in basic electricity, perhaps the two most common types of circuits are parallel and series.

A parallel-connected circuit is one in which the current divides into two or more flows with at least one load on each flow, whereas a series circuit has only one flow that passes through two or more consecutive loads. The input voltage to a parallel-connected circuit stays constant - so every branch of the circuit gets the same voltage from the power supply - but there is a different current flowing in each branch dependant on the resistance of the loads in that branch. Overall, no current gets lost because any current entering a particular junction (leading to branches) is always equal to the current leaving that junction.

In a series-connected circuit the input current stays constant and the voltage is divided amongst the loads which are connected like links in a chain: each load component (a light, a resistor, etc.) is connected "head to tail" to the next one in the series circuit.

A more complete answer

Actually there are four types of circuit, not two. These are series circuits, parallel circuits, series-parallel circuits, and complex circuits.

'Complex circuits' (which are not necessarily complicated) describe any circuit that is not series, parallel, or series-parallel - a Wheatstone Bridge is an example of a complex circuit.

The techniques for solving series, parallel, and series-parallel circuits cannot be used for solving complex circuits. Instead, network theorems, such as Thevenin's and Norton's Theorems must be used.

Answer 2

If you're talking about modelling electronic circuits, then the two basic representations are Norton's equivalent and Thevenin's equivalent