Here's why:

* Series Circuit: In a series circuit, the components (like light bulbs) are connected in a single, continuous path. The electricity has only one path to travel through.

* Current Flow: Current represents the flow of electrical charge. Since there's only one path, the same amount of charge must flow through each component in the circuit.

Think of it like a single-lane road: If 10 cars are on the road, all 10 cars have to travel on the same path at the same time.

Important Note: While the current is the same, the brightness of the bulbs may differ. This depends on the resistance of each bulb. A higher resistance bulb will have a lower brightness because it restricts the current flow more.