Current in a series circuit

What is a series circuit?

In a series circuit, the components (lamps, resistors, etc.) are connected one after the other, forming a single loop. The current has only one possible path to follow.

Ohm’s law in a series circuit

In a series circuit, the current is the same at every point in the circuit. Whether an ammeter is placed before the first bulb, between the two bulbs, or after the second bulb, it will always read the same value.

This law is expressed as follows: I = I1 = I2 = ... = In

Practical example

Two bulbs, L1 and L2, are connected in series with a battery. The current is measured successively at three points in the circuit:

Position of the ammeter	Measured current
Before L1	0.30 A
Between L1 and L2	0.30 A
After L2	0.30 A

The three measurements are identical: nothing is lost or added along a series circuit.

A common misconception

Many pupils mistakenly believe that the current ‘wears out’ as it passes through the bulbs and that the current decreases after each load. This is incorrect: electric charges are neither created nor destroyed; the current remains constant in a series circuit.