Why This Matters
Series circuits are one of the two fundamental ways to connect electrical components. Understanding them will help you predict what happens when a component fails and how voltage and current behave in real devices.
Components in a Line
In a series circuit, every component is connected end-to-end, forming a single path for current. There is only one route from the source, through each component, and back again.
Think of a one-lane road. Every car must follow the same path in the same order — there are no side streets or shortcuts.
Current Stays the Same
Because there is only one path, the same amount of current flows through every component. If 2 amps flows through the first resistor, 2 amps also flows through the second, the third, and so on.
Voltage Divides
While current stays constant, voltage is shared among the components. Each component “uses up” a portion of the total voltage. The individual voltage drops add up to the total voltage of the source.
For example, a 9 V battery powering three identical bulbs in series gives each bulb about 3 V.
If One Fails, All Stop
This is the most important practical fact about series circuits. If any single component breaks or is removed, the loop is broken and current stops flowing everywhere.
Real World Example
Think of old-fashioned Christmas lights — the kind where one burned-out bulb made the entire string go dark. Those bulbs were wired in series. When one filament broke, the single path was interrupted and every bulb lost power. (Modern Christmas lights use a shunt that bypasses a dead bulb, but the underlying wiring is still series.)
Common Beginner Mistake
Beginners often assume that the first component in a series circuit “uses up” all the current, leaving less for the others. That is not how it works. Current is the same everywhere in a series loop. What gets divided is the voltage, not the current.
Key Terms
- Series Circuit — A circuit in which components are connected end-to-end so that the same current passes through each one.
Exercise
Three resistors are connected in series to a 12 V battery. Each resistor has the same resistance. How much voltage appears across each resistor?
Show Answer
4 V across each resistor. In a series circuit the total voltage divides equally among identical components: 12 V ÷ 3 = 4 V.
Recap
- In a series circuit, components form a single path for current.
- Current is the same through every component.
- Voltage divides among the components.
- If one component fails, the entire circuit stops working.