Series circuits
Why does the same current flow through both series resistors?
One comparison at a time
Experiment with a guide
Use a single current path to relate total resistance, voltage drops and power.
Comparison 1 of 3
Follow a closed circuit
Start with a 12 V source, R₁ of 4 Ω and R₂ of 8 Ω. Total resistance is 12 Ω and the common current is 1 A. There is no branch where current splits.
The voltage drops are 4 V and 8 V: they add to the source’s 12 V. Current is 1 A in both resistors.
You are exploring other values. You can continue freely or apply this comparison’s values again.
How to read this drawing
The source on the left has + and − poles. The wire closes a single path through R₁ and R₂. The arrow and points indicate conventional current direction; their motion is symbolic, with no charge-speed scale. Read I in amperes, each voltage in volts and each resistance in ohms. The resistor boxes do not represent their physical size.
From drawing to graph
What changes? Let’s compare.
A line shows the relationship between quantities. The point marks your choice or the instant in the animation. First read the axis names and units.
One experiment at a time
Save. Change. Compare.
Save the current values, change one quantity and observe both lines on the same graph. The saved line is dashed. The attempt stays in this browser.
Compare the chosen values
What if… Double voltage while keeping the resistors fixed. Then increase only R₁ and compare current and both voltage drops.
What is happening?
A series circuit has a single path. Current is the same in both resistors and their voltage drops add to the source voltage.
The ideal source establishes a potential difference. Each resistor opposes the flow of current: in series, resistances add. By Ohm’s law, current is source voltage divided by total resistance. The resistor with greater resistance has a greater voltage drop and dissipates more power, because the same current passes through both.
V — voltage (V) · I — current (A) · R — resistance (Ω) · P — power (W)
The model and its limits
Ideal direct-current source, resistance-free wires and two ohmic resistors in series. The model shows the steady state. Markers indicate the conventional current direction outside the source, from positive to negative; their motion is symbolic and does not measure charge drift velocity.