Electricity needs a complete path (circuit) to flow. How you connect components creates two basic circuit types:
Battery → Bulb 1 → Bulb 2 → Bulb 3 → Battery
One path for electricity. All bulbs share the same current.
Battery → Bulb 1 ┐
Battery → Bulb 2 ┼→ Battery
Battery → Bulb 3 ┘
Multiple paths. Each bulb gets full voltage.
- Current (I) – measured in Amperes (A). The flow of electric charge.
- Voltage (V) – measured in Volts (V). The "pressure" pushing current.
- Resistance (Ω) – measured in Ohms. Opposition to current flow.
- Series: Current is the same everywhere. Voltage is shared (split).
- Parallel: Voltage is the same everywhere. Current is shared (split).
- 🔋 2-4 batteries (AA or D-size, 1.5V each) – can be used or new
- 💡 3 small light bulbs (2.5V or 3V – from old torches/flashlights)
- 🔌 3 bulb holders (or make from cardboard and paperclips)
- 🪢 Connecting wires – insulated copper wire, stripped at ends. Old phone charger cables work!
- 📦 Battery holder – optional (or use rubber bands and cardboard)
- ✂️ Wire strippers or scissors (adult supervision)
- 📝 Notebook – for observations and circuit diagrams
💰 Total cost: 0-200 KES (bulbs may be the only purchase; batteries can be old remote control batteries).
🔗 Circuit 1: Series Connection
What happens in series? All bulbs are connected one after another in a single path. The same current flows through every bulb. Each bulb gets only a share of the battery's voltage, so bulbs are dimmer than in parallel.
First, draw your series circuit. Connect: Battery positive (+) → Bulb 1 → Bulb 2 → Bulb 3 → Battery negative (-). This is one continuous loop.
✏️ Always draw your circuit before building. Label: battery, bulbs, wires.
Place your 3 bulb holders on a board or table. Connect wire from battery positive to the first bulb holder. Then wire from first bulb holder to second bulb holder. Then second to third. Finally, wire from third bulb holder back to battery negative.
🔌 Each bulb has two terminals – connect them in sequence.
Connect the battery. All three bulbs should light up, but you will notice they are dimmer than a single bulb alone. Record: How bright are they? (Rate 1-5, 5 being very bright).
💡 Brightness level in series: usually 2/5 with 3 bulbs.
Unscrew or disconnect ONE bulb. What happens? ALL bulbs go out! This is the key property of series circuits – the path is broken, so electricity stops everywhere.
🎄 This is why old Christmas lights were frustrating – one broken bulb made the whole string dark!
- Current (I) is the same through all components: I₁ = I₂ = I₃
- Voltage is divided: V_total = V₁ + V₂ + V₃
- Resistance adds: R_total = R₁ + R₂ + R₃
- If one bulb breaks, ALL go out – one break, circuit broken
- Bulbs are DIMMER than parallel (voltage is shared)
🔀 Circuit 2: Parallel Connection
What happens in parallel? Each bulb has its own direct connection to the battery. Current flows through multiple paths. Each bulb gets the FULL battery voltage, so bulbs are brighter than in series.
Draw your parallel circuit. All bulb positive terminals connect together and go to battery positive. All bulb negative terminals connect together and go to battery negative.
✏️ Think of it like separate lanes on a road – each bulb has its own path.
Connect a wire from battery positive to a "bus bar" (create a connection point). Connect the positive terminal of EACH bulb to this bus bar. Then connect a wire from battery negative to another bus bar. Connect the negative terminal of EACH bulb to this second bus bar.
🔌 All bulbs share the same connection points but have separate paths.
Connect the battery. All three bulbs should light up. They will be brighter than in the series circuit because each gets the full battery voltage. Record brightness: usually 4/5 or 5/5.
💡 In parallel, adding more bulbs does NOT make them dimmer (until you exceed battery capacity).
Unscrew or disconnect ONE bulb. What happens? The OTHER bulbs stay LIT! This is the key property of parallel circuits – each bulb has its own path, so one failure doesn't affect the others.
🏠 This is why your home uses parallel wiring – you can turn off one light without affecting others!
- Voltage (V) is the same across all branches: V₁ = V₂ = V₃ = V_battery
- Current is divided: I_total = I₁ + I₂ + I₃
- Total resistance decreases as you add more bulbs
- If one bulb breaks, others continue working – multiple paths
- Bulbs are BRIGHTER than series (each gets full voltage)
| Property | Series Circuit | Parallel Circuit |
|---|---|---|
| Brightness of bulbs | Dimmer (voltage shared) | Brighter (full voltage each) |
| If one bulb fails | ALL bulbs go out | Others stay on |
| Number of current paths | One path | Multiple paths |
| Current (I) | Same everywhere | Splits between branches |
| Voltage (V) | Divided between bulbs | Same across each bulb |
| Adding more bulbs | Bulbs get dimmer | Brightness stays same |
| Real-world example | Old Christmas lights | Home wiring, school lights |
| Test | Series Circuit Observation | Parallel Circuit Observation |
|---|---|---|
| Brightness with 1 bulb | _______ (1-5 scale) | _______ (1-5 scale) |
| Brightness with 2 bulbs | _______ (1-5 scale) | _______ (1-5 scale) |
| Brightness with 3 bulbs | _______ (1-5 scale) | _______ (1-5 scale) |
| Remove bulb 1 – what happens? | _______________ | _______________ |
| Remove bulb 2 – what happens? | _______________ | _______________ |
| Add a 4th bulb (if possible) | _______________ | _______________ |
- No bulbs light: Check battery connection polarity (+ to +, - to -). Make sure wires are stripped and making good contact.
- One bulb not lighting in series: That bulb may be broken. Replace it.
- Bulbs very dim: Battery may be weak. Replace with fresh batteries.
- Wires get hot: You may have a short circuit (wire touching directly from battery + to - without bulb). Check connections.
- Parallel circuit: some bulbs brighter than others: Check wire connections – loose contact reduces brightness.
- Add a switch: Insert a simple switch (two paperclips touching) into both circuits. Compare where you need to place the switch to turn all bulbs on/off.
- Measure with multimeter: If your school has a multimeter, measure voltage across each bulb in series vs parallel. Record the difference.
- Add more batteries: Connect two batteries in series (4.5V total) and observe how brightness changes in both circuits.
- Draw professional diagrams: Use standard circuit symbols (—|∣— for battery, —○— for bulb) to draw both circuits.
- Calculate theoretically: If each bulb is 3Ω and battery is 3V, calculate current in series (I = V/R = 3/9 = 0.33A) vs parallel.
| Criteria | Exceeds (5) | Meets (4) | Approaching (3) | Below (2-1) |
|---|---|---|---|---|
| Circuit Construction}, | Both circuits built correctly. All connections secure. Bulbs light as expected. No short circuits. Diagrams match physical circuits.}, | Both circuits functional, minor loose connections. Works after adjustment.}, | One circuit functional, other has errors. Multiple attempts needed.}, | Neither circuit works properly.}, |
| Observations & Data}, | Complete observation log with brightness ratings. Successfully tests bulb removal in both circuits. Records voltage/current differences.}, | Most observations recorded. Bulb removal test completed.}, | Partial observations. Missing key tests.}, | No data recorded.}, |
| Understanding of Concepts}, | Explains current and voltage in both circuits. Identifies real-world applications (home wiring vs Christmas lights). Uses correct terminology. Calculates values.}, | Explains basic differences between series and parallel. Can identify examples.}, | Partial explanation. Confuses some concepts.}, | Cannot explain difference between circuits.), |
| Documentation & Diagrams}, | Clear circuit diagrams with standard symbols. Photos of both working circuits. Written conclusion comparing brightness, failure mode, and applications.}, | Diagrams present. Photos of circuits. Basic conclusion.}, | Missing diagrams or photos. Weak conclusion.}, | No documentation.), |
- Create a combination circuit: two bulbs in parallel, connected in series with a third bulb. Predict brightness before building.
- Use a multimeter to measure and record actual voltage across each bulb in both circuits.
- Research and explain: Why do hospitals and data centres use parallel circuits with backup systems?
- Draw a wiring diagram of ONE ROOM in your home showing how lights are wired in parallel.
Where Electricity Knowledge Leads
Understanding circuits is the foundation for every electrical career. Electricians wire homes, schools, and businesses – they must know that homes use PARALLEL wiring so lights work independently. Electrical engineers design power grids, electronics, and machines. In Kenya, companies like Kenya Power, KPLC contractors, and solar installation companies constantly need trained technicians. Electrical tradespeople earn 30,000-80,000 KES/month. This simple project is your first step toward a career in electricity!
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Take this guide to your physics lab. Use the observation log to record your results.