Mission 1/18Build0/18 ✓
Light the bulb
Put a material that lets charge through into the gap and close the switch. The bulb should light.
Try it in the simulation — the mission completes on its own when you reach the goal.
Circuit
Open
switch is open
Current
0.000A
0.0000 C of charge per second
Bulb power
0.00W
0.00 J every second
Sample
Copper
R ≈ 0.002 Ω
Test log · 0/11
Close the switch and test a material.
electron (−) · speed ∝ current
Setting up the scene…
0.00 W
Copper · conductor
Switch: open
4.5 V · 3 × 1.5 V
Ammeter
0.000 A
0.000 A
0.000 A
Concepts
A closed circuit is an unbroken loop
A bulb lights only if charge has an unbroken path from the battery's + terminal, through the bulb, and back to −. A switch is a gate that opens and closes this loop. One wire is not enough: charge can leave but has no way back.
A gap anywhere in the loop (open switch, unscrewed bulb, insulator) makes the current zero everywhere.
A gap anywhere in the loop (open switch, unscrewed bulb, insulator) makes the current zero everywhere.
Conductors and insulators
Every material contains charged particles; the difference is whether they can move. In metals and graphite some electrons roam freely: these are conductors. In plastic, glass, wood, rubber and air the charges are held tightly by their atoms: these are insulators.
Water is a neat case: pure water barely conducts, but dissolving salt releases ions that carry the current.
Water is a neat case: pure water barely conducts, but dissolving salt releases ions that carry the current.
Current is the rate of charge flow
Wires are already full of charge — a battery doesn't make charge, it pushes the charge that is already there. Current is how much charge passes a point each second: 1A=1C/s. Bulbs don't use up charge; as much returns to the battery as leaves it. In the sim the particles' speed is proportional to the current (up to a top speed for very large currents), while their number never changes.
I=tQ
Two arrows for the same current
Before electrons were discovered, scientists chose + → − as the direction of current: this is conventional current. The particles that really move in a wire are electrons, which are negative and travel − → +. Both describe the same current; use the toggle in the dock to watch either one.
What this lab simplifies
The battery is ideal: no internal resistance, so its voltage doesn't depend on the current (a real battery's terminal voltage sags a little at high current). Connecting wires and the ammeter have zero resistance, the voltmeter infinite. Bulbs are treated as fixed resistances; a real filament's resistance rises as it heats up.
Voltage: energy given to each coulomb
A battery's voltage tells how much energy it gives each coulomb of charge passing through it: 1V=1J/C. Voltage doesn't flow; it is a difference between two points, which is why a voltmeter always connects to two points. Cells in series add up: each one adds 1.5V.
Turn on potential colours to see that the potential stays the same along a wire and only drops across bulbs and resistors.
Turn on potential colours to see that the potential stays the same along a wire and only drops across bulbs and resistors.
V=QE
Ohm's law
For a resistor at constant temperature, current is directly proportional to voltage. The I–V graph is a straight line through the origin with slope 1/R: a larger resistance gives a flatter line. Double the voltage and the current doubles; double the resistance and the current halves.
I=RVV=IR
Reading resistor colour bands
The first two bands are digits, the third is the multiplier (a power of 10), the fourth is the tolerance.
black 0 · brown 1 · red 2 · orange 3 · yellow 4 · green 5 · blue 6 · violet 7 · grey 8 · white 9
A gold multiplier band means ×0.1. Example: yellow-violet-black-gold = 47×1=47Ω, 5 % tolerance.
black 0 · brown 1 · red 2 · orange 3 · yellow 4 · green 5 · blue 6 · violet 7 · grey 8 · white 9
A gold multiplier band means ×0.1. Example: yellow-violet-black-gold = 47×1=47Ω, 5 % tolerance.
Ammeters and voltmeters
An ammeter goes in series and has almost zero resistance: it measures the current without changing it. A voltmeter goes in parallel with the part being measured and has a huge resistance: it draws almost no current.
A surprise: put a voltmeter across an open switch and it reads the full battery voltage — all of the "push" is across that gap.
A surprise: put a voltmeter across an open switch and it reads the full battery voltage — all of the "push" is across that gap.
Series: one path
A series circuit gives charge only one path, so the current is the same at every point. The battery voltage is shared between the parts and resistances add. A bigger resistance takes a bigger share of the voltage. Unscrew one bulb and the loop breaks, so all go out. The bulb nearest the battery isn't brighter — the current is the same.
Req=R1+R2+R3V=V1+V2+V3
Parallel: many paths
In parallel each branch is wired straight across the battery, so every branch has the same voltage. The current splits at a junction and joins again afterwards: I=I1+I2+I3. Each new branch is another path, so the equivalent resistance falls and the total current rises. Open one branch and the others stay lit.
Req1=R11+R21+R31
Power and brightness
Power is how fast energy is transferred: 1W=1J/s. A bulb's brightness follows its power.
In series the current is the same in both, so P=I2R: the bigger resistance is brighter. In parallel the voltage is the same, so P=V2/R: the smaller resistance is brighter. So "bigger resistance is always dimmer" is false — it depends on how they're connected.
In series the current is the same in both, so P=I2R: the bigger resistance is brighter. In parallel the voltage is the same, so P=V2/R: the smaller resistance is brighter. So "bigger resistance is always dimmer" is false — it depends on how they're connected.
P=VI=I2R=RV2
What sets a wire's resistance?
A longer wire is a longer road for charges: resistance is proportional to length. A thicker wire is a wider road: resistance is inversely proportional to cross-section. Material matters too: resistivity ρ is tiny for copper and about 65 times larger for nichrome — which is why heater elements are nichrome.
R=ρAL
Skills and curriculum
Open and closed circuits
Grades 4–6Explain that current flows only around a closed loop, and the difference between conductors and insulators.
Not started
MEB Grade 4 · Simple Electric Circuits · F.4.7.1.1, F.4.7.1.2MEB Grade 6 · Electrical Conduction and Resistance · FB.6.6.1NGSS 4-PS3-2
Ohm's law
Grades 9–10Use V = I·R to find voltage, current or resistance.
Not started
MEB Grade 10 · Electricity · FİZ.10.3.3CCSS HSA-CED.A.4
Series circuits
Grades 9–10Use that series current is the same everywhere, voltage is shared, and resistances add.
Not started
MEB Grade 10 · Electricity · FİZ.10.3.4NGSS HS-PS3-1
Parallel circuits
Grades 9–10Use that parallel branches share voltage, currents add, and equivalent resistance drops.
Not started
MEB Grade 10 · Electricity · FİZ.10.3.4NGSS HS-PS3-1
Electric power and brightness
Grades 9–10Compare bulb brightness and energy use with P = V·I = I²·R.
Not started
MEB Grade 10 · Energy · FİZ.10.2.2NGSS HS-PS3-1
What sets resistance
Grades 6–10Explain how a wire's length, cross-section and material set its resistance (R = ρ·L/A).
Not started
MEB Grade 6 · Electrical Conduction and Resistance · FB.6.6.2, FB.6.6.3