⚡ PhET — Circuit Construction Kit
Grade 7 · Electricity · Part 2

Open circuits,
closed circuits.

In Part 1 you learned the components. Now you will build real circuits, test conductors and insulators yourself in PhET, and discover why a circuit must be closed for current to flow.

E2 · Explore

Open vs Closed Circuits

Tap the switch buttons below to see what happens to the circuit — and understand why position of the switch matters for current flow.

🔓 Open Circuit
The switch creates a gap in the circuit.
Current cannot flow — the path is broken.
The lamp stays OFF. Energy cannot reach the receiver.
🔒 Closed Circuit
The switch completes the circuit loop.
Current flows freely — the path is complete.
The lamp lights ON. Energy reaches the receiver.
📝 Record Your Observations
Quick Check
A lamp in a circuit is off. The battery is working. The most likely reason is:
AThe lamp needs more voltage
BThe switch is open — the circuit is broken
CThe wire is too long
DThe lamp is too bright
E2 · Materials Test

Test: Conductor or Insulator?

In a real circuit, the material you place in the gap determines whether current flows. Tap each material to insert it and observe the result — just like the PhET sim will let you do.

Tap a material to test it in the circuit
Predict First
Before testing — which of these would allow current to flow and light the lamp?
ARubber eraser
BIron nail
CPlastic ruler
DDry wood
E3 · Build

Build Your Circuit in PhET

Now use the PhET simulator to build a real open and closed circuit. Follow the steps below, then take a screenshot of your final circuit to submit.

⚡ Circuit Construction Kit: DC

University of Colorado Boulder · Free simulation

1
Add a battery, lamp, switch and wires
Drag them from the toolbox. Connect wires to form a complete rectangular loop.
2
Open the switch — observe the lamp
What happens? Record your observation below.
3
Close the switch — observe the lamp
What happens now? Is the lamp on?
4
Replace a wire with a conductor/insulator
In PhET, drag different materials (pencil lead, eraser, coins) into the circuit gap. Which ones let current flow?
5
Take a screenshot of your final circuit
In PhET: click the camera icon (top right of simulation) → save the image → upload it in the next section.
📝 PhET Observations
E3 · Screenshot

Upload Your Circuit Screenshot

Take a screenshot of your completed PhET circuit, then upload it here. It will be saved directly to Ahmad's Google Drive so he can review your work.

📸
Tap to upload your PhET screenshot
Accepted: PNG, JPG, JPEG · Max size: 5MB
Your image is uploaded securely · a link is saved in Ahmad's grade sheet
Circuit preview
💡 How to take a PhET screenshot: Inside the PhET simulation, look for the camera icon 📷 in the top-right corner of the simulation window. Click it — a PNG image will download automatically. Then come back here and upload it.
E4 · Practice

Apply What You Discovered

Three questions based on your PhET investigation.

Question 1 · Circuit Type
In your PhET circuit, when the switch was open, what type of circuit did you have?
AA closed circuit — current was flowing
BAn open circuit — the path was broken and no current flowed
CA short circuit — too much current
DA parallel circuit
Question 2 · Conductors in PhET
In the PhET simulation, you placed a pencil (graphite) in the circuit gap. The lamp lit up. This means graphite is:
AAn insulator — it blocked the current
BA conductor — it allowed current to flow through it
CA switch — it controls the circuit
DA generator — it produces electricity
Question 3 · Explain
In your own words — explain why a circuit must be closed for the lamp to light up. Use what you observed in PhET.
Your answer is saved when you submit.
E5 · Submit

Submit Your Work

Enter your name and class, then submit everything to Ahmad's grade sheet — including your circuit screenshot.

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Your Score

Ahmad reviews your circuit screenshot and written answers in class.