Circuit Lab Division B: a middle school starter guide
- 192parts on the bench
- 25boards running now
- 1.00xreal time, on every board
If you are new to Circuit Lab, or new to coaching it, start here. Science Olympiad lists Circuit Lab for Division B in the 2027 season. This guide covers the ideas a middle school team needs first, in the order that makes them easy: what makes a circuit work, series and parallel, and how to use a meter. Each idea has a circuit you can try in your browser.
Your coach should also read the official Division B rules at soinc.org. They say exactly what the event covers this year, and they change from season to season.
A circuit is a loop
Electricity only flows when there is a complete path from one side of the battery, through the parts, and back to the other side. That path is called a closed circuit. Break it anywhere, with a switch or a loose wire, and it becomes an open circuit, and nothing flows.
Open the first circuit. It has a switch, a resistor and an LED. Click the switch and the LED lights, because you closed the loop. Click it again and the loop opens. The resistor is there to limit the current so the LED is not damaged.
Voltage, current and resistance
Voltage (measured in volts, V) is the push that makes charge move. Current (in amps, A) is how much charge flows past a point each second. Resistance (in ohms) is how hard it is for current to get through a part.
The three are linked by Ohm’s law: voltage equals current times resistance, or V = I x R. If you know any two, you can find the third. A 6 V battery across a 200 ohm resistor pushes 6 / 200 = 0.03 A, which is 30 mA.
Series and parallel lamps
The circuit at the top of this page has four identical lamps (LEDs with their own resistors) and a switch that sends 6 V to one side or the other. On the left, two lamps are in series: one loop, one after the other. On the right, two lamps are in parallel: each has its own loop to the battery.
Try it. With the series side on, both lamps are dim and the meter shows the battery supplying about 5.6 mA. Flip the switch and the parallel lamps are bright and the battery supplies about 36 mA. In series the two lamps share the battery’s push; in parallel each lamp gets all of it, which is also why parallel lamps drain a battery faster.
Now delete one lamp on each side. On the series side, the other lamp goes out, because you broke the only loop. On the parallel side, the other lamp stays lit, because it still has its own loop. That is why the lights in your house are wired in parallel.
Using the meter
A multimeter is how Circuit Lab asks you to prove what you know. To measure voltage, touch the two leads on either side of a part while the circuit is on. To measure current, the meter has to become part of the loop, so the current flows through it.
The divider circuit has three equal resistors from 5 V to ground and a meter on one of them. It reads about 1.67 V, one third of the supply, because three equal resistors share the voltage equally. Move the red lead up one resistor and it reads twice that. The multimeter guide goes further, step by step.
Five questions to check yourself
1. A switch is off. Is the circuit open or closed?
2. Two identical lamps are in series on a battery. One burns out. What happens to the other?
3. Are two identical lamps brighter in series or in parallel on the same battery?
4. A 9 V battery is connected across a 300 ohm resistor. What is the current?
5. Where do you put a meter to measure current: across a part or in the loop?
Answers: 1. Open. 2. It goes out too. 3. In parallel. 4. 0.03 A, or 30 mA. 5. In the loop, in series.
Tips for coaches
Students learn this fastest by predicting and then checking. Ask for a prediction before every click. A team member who can explain why the parallel lamps are brighter is worth more on test day than one who memorized it.
Pair this with real parts if you can: a battery pack, a few bulbs or LEDs with resistors, and one inexpensive meter are enough. Keep to batteries of 9 V or less. When your team is ready for more, the full Circuit Lab study guide and the practice test are the next steps.
Units and prefixes
Many missed points come from units, not physics. Milli means one thousandth, so 25 mA is 0.025 A. Kilo means one thousand, so 4.7 k ohms is 4,700 ohms. Micro means one millionth, so 100 uF is 0.0001 F.
Convert everything to plain volts, amps and ohms before you use Ohm’s law, then convert the answer back if the question asks for it. A quick check: 5 V across 1 k ohms is 5 mA, and volts divided by kilohms always gives milliamps. Practice that until it is automatic.
Questions
Is Circuit Lab in Division B for 2027?
Yes. Science Olympiad’s 2027 event list includes Circuit Lab in both Division B and Division C. Confirm with your own regional or state tournament.
Why use LEDs instead of light bulbs?
LEDs with resistors behave like bulbs for series and parallel: shared voltage makes them dimmer. They are also what most school kits use now.
Build this for real
Open the editor, change a value and watch the number move with it. Nothing to install, and no account needed.