Circuit Builder
Circuit Builder is a free interactive simulation from StudyFi Lab. It runs right in your browser, with no sign-up and nothing to install.
Build circuits and watch Ohm’s and Kirchhoff’s laws at work
Experiments
Free build
Build any circuit on the breadboard. Current flows only around a closed loop from the + pole of the battery back to its − pole. Ohm’s law I = U/R sets its size, and a bulb glows the brighter the more power P = U·I = I²·R it takes.
Try this: Build a loop with a battery, a switch and a bulb. Then add a second bulb in series and watch both of them dim.
Series vs parallel
On the left, two equal bulbs are in series: they share the battery voltage, each gets U/2, the current is halved and each glows with only a quarter of the power (P = U²/R). On the right they are in parallel: each gets the full voltage, glows fully, and the battery delivers twice the current, because R = R₁·R₂/(R₁ + R₂).
Try this: Compare ammeters A1 and A2. Then remove one bulb on each side: in series both go out, in parallel the other keeps glowing.
Kirchhoff’s laws
First law: the current flowing into a junction equals the current flowing out, ΣI = 0 — ammeters A1, A2 and A3 meet at one node. Second law: around a closed loop the voltages add up to zero, ΣU = 0 — the battery voltage V1 equals the drops across R1 and R3 (V2 + V3). A negative reading means the current flows against the meter’s arrow.
Try this: Change the voltage of battery B2 until ammeter A2 reads zero. Then keep going and watch its sign flip.
Bulb puzzle
All bulbs are powered by the same battery. In series the same current flows through each bulb, so the one with the larger resistance takes more power (P = I²·R). In parallel each bulb has the same voltage, so the one with the smaller resistance glows brighter (P = U²/R). A bulb in the main branch carries the sum of the branch currents.
Try this: Guess which bulb will glow the brightest, press Reveal, then move on to the next puzzle.
Frequently asked questions
What is Circuit Builder?
Circuit Builder is a free interactive simulation from StudyFi Lab. It runs right in your browser, with no sign-up and nothing to install. Build circuits and watch Ohm’s and Kirchhoff’s laws at work
Is Circuit Builder free?
Yes. Circuit Builder is completely free. It works in the browser on computers, tablets and phones, and you do not need an account.
What can I explore in Circuit Builder?
Free build, Series vs parallel, Kirchhoff’s laws, Bulb puzzle.
What does the “Free build” experiment show?
Build any circuit on the breadboard. Current flows only around a closed loop from the + pole of the battery back to its − pole. Ohm’s law I = U/R sets its size, and a bulb glows the brighter the more power P = U·I = I²·R it takes.
What does the “Series vs parallel” experiment show?
On the left, two equal bulbs are in series: they share the battery voltage, each gets U/2, the current is halved and each glows with only a quarter of the power (P = U²/R). On the right they are in parallel: each gets the full voltage, glows fully, and the battery delivers twice the current, because R = R₁·R₂/(R₁ + R₂).
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