Your first circuit.
Put Ohm’s law to work.

01 / CONNECT

Build a closed loop

You need a 9 V battery, a 1 kΩ resistor, and two wires. Both parts are available on the shelf. A resistor limits current; a wire alone across the battery makes a short circuit.

1. Open the electronics lab and place the battery and resistor on the bench. No account is needed.
2. Connect the battery’s positive terminal to either resistor terminal. Select one terminal, then the other, to make a wire.
3. Connect the other resistor terminal to the battery’s negative terminal. This completes the loop. An ordinary resistor works in either direction.

On a computer, aim the crosshair at the part or terminal and interact. Press Escape to pause and release the mouse. On a touch screen, tap the part or terminal. See the controls guide if you need help placing parts.

02 / PREDICT

Use Ohm’s law: I = V / R

For an ideal resistor, voltage V equals current I multiplied by resistance R. Rearranging gives I = V / R. Use volts, amperes and ohms in the calculation.

This is an ideal estimate. The simulator includes battery internal resistance, wire resistance and the meter’s effect on the circuit, so the measured value can be slightly different. Use the actual voltage across the resistor for a closer prediction.

A lamp is different from a fixed resistor: its filament resistance changes as it heats. Do not expect one constant resistance value to describe a lamp at every voltage.

03 / MEASURE

Voltage goes across. Current goes through.

Measure voltage

Select DC voltage on the multimeter. Put the red probe on the resistor terminal connected to the battery’s positive side, and the black probe on the other end. The reading should be close to 9 V. Reversing the probes changes the sign.

Measure current

Remove one wire to open the loop. Set the meter to current, then connect its probes across that gap so current passes through the meter. Expect a reading close to 9 mA. Do not put a current-mode meter directly across the battery: its low resistance makes a near-short and can open the simulated fuse.

Measure resistance

Disconnect the battery and isolate the resistor before selecting resistance mode. Measure across the resistor’s two terminals. An ohmmeter uses its own test signal and should not be connected to a powered circuit.

Readings need a short simulated settling interval. The multimeter guide explains settling, range and fuse messages.

04 / COMPARE

Try series and parallel resistors

Use the 1 kΩ resistor and a 220 Ω resistor from the shelf with the same 9 V battery. The following values assume ideal parts and no meter loading.

Series: one path for current

Connect battery positive → 1 kΩ → 220 Ω → battery negative. The resistances add: 1,000 + 220 = 1,220 Ω. Current is approximately 9 ÷ 1,220 = 7.38 mA through both resistors. Expect about 7.38 V across the 1 kΩ part and 1.62 V across the 220 Ω part.

Parallel: two paths between the same points

Connect one end of each resistor to battery positive, and the other end of each to battery negative. Each branch has nearly the full battery voltage. Ideal branch currents are 9 mA through 1 kΩ and 40.9 mA through 220 Ω; total current is about 49.9 mA.

Notice the difference: in series, both resistors carry the same current. In parallel, they share the same voltage, while current splits between the branches.

05 / TROUBLESHOOT

If the reading is not what you expected

• No current: check that every wire ends on a terminal and there is a complete return path to the battery.
• Negative reading: check the probe direction. A negative sign can simply mean the probes are reversed.
• Zero voltage across a resistor: check whether a wire bypasses it or both probes touch the same electrical point.
• Fuse or overload message: check the meter mode, its placement, and component ratings before resetting the lab.
• A small difference from your calculation: account for source and wire resistance and the meter itself. A simulation with non-ideal components need not match an ideal calculation exactly.

When the basic circuit works, try adding a switch or observing a changing signal with the oscilloscope. The signals and components guide introduces the next tools.