⚡ PhET — Circuit Construction Kit
Grade 7 · Science · Unit: Electricity

How does a
circuit work?

Electricity powers everything around us — from the lamp on your desk to the screen you're reading right now. In this lab you'll discover the components, build real circuits, and understand what makes electricity flow.

⚡
Generators
💡
Receivers
🔗
Conductors
🔄
Switches
E2 · Components

Circuit Components

Every electric circuit needs specific components to work. Tap each card to learn about its role, real-world examples, and conventional symbol.

Quick Check · Components
Which component in a circuit converts electrical energy into light and heat?
AConnecting wire
BSwitch
CLamp (light bulb)
DDry cell (battery)
E2 · Symbols

Conventional Circuit Symbols

Engineers worldwide use the same symbols to draw electric circuits. These are the symbols you need to know for Grade 7.

Symbol Recognition
The symbol below shows a circle with an X inside. What component does it represent?
AMotor
BBattery (dry cell)
CLamp (light bulb)
DSwitch
E2 · Materials

Conductors & Insulators

Not all materials allow electricity to pass through them. Understanding the difference is key to safe circuit design.

⚡ CONDUCTOR
A material that allows electric current to flow through it easily.
Why? It has free electrons that can move.
Examples: Copper, aluminium, iron, silver, water (impure)
🚫 INSULATOR
A material that does NOT allow electric current to flow through it.
Why? Its electrons are tightly bound — cannot move freely.
Examples: Rubber, plastic, glass, wood, ceramic, dry air
⚡ Live Experiment — Insert a material into the circuit gap
Tap a material below to insert it between the terminals. Watch what happens to the current and the lamp!
Select a material above to test it
🎯 Sorting Game — Tap a material then tap the correct zone
⚡ Conductors
Tap a chip then tap here
🚫 Insulators
Tap a chip then tap here
E3 · Switch

The Switch — Open & Closed

A switch controls the flow of current by either completing or breaking the circuit. Tap the switches to see what happens.

🔓 Open Switch
The circuit is broken. No current can flow.
The lamp goes off. Energy cannot travel around the loop.
🔒 Closed Switch
The circuit is complete. Current flows freely.
The lamp lights up. Energy travels from generator → receiver.
True or False
When a switch is open, current still flows but very weakly.
ATRUE — the current is just reduced
BFALSE — an open switch completely stops current flow
E3 · Cells & Receivers

Cells & Receiver Behaviour

The number of cells (dry cells) connected determines how much voltage the circuit has — and directly affects how strongly a receiver works. Experiment below!

⚡ Interactive — Choose number of cells and receiver
—
Select cells above
0 CELLS
No source of energy. Switch can be anything — nothing works.
1–2 CELLS (rated)
Normal operation. Receiver works as designed — rated power.
TOO MANY CELLS
Overvoltage! The receiver overheats and may burn out permanently.
E3 · Simulation

PhET Circuit Simulation

Build and test real circuits in the PhET simulator. Try connecting different components and observe how changing cells affects the brightness of the lamp.

⚡ Circuit Construction Kit: DC

Build virtual circuits with batteries, wires, light bulbs, resistors and switches. This simulation was developed by the University of Colorado Boulder.

Try these in the simulation:
1. Connect one battery → one lamp → one switch. Close the switch — does the lamp light?
2. Add a second battery. What happens to the lamp brightness?
3. Add a third battery. What do you observe? Can you explain why?
4. Try connecting two lamps. What happens to each lamp's brightness?
E3 · Key Concepts

⚡ Voltage & Current

The two most important — and most confusing — ideas in electricity. Let's crack them with animations.

⚡ Electric Current (I)
Definition: The flow of electrons through a conductor.

Water pipe analogy: Current = the flow rate of water (litres/second).

Unit: Ampere (A)

Effect: More current → brighter lamp / faster motor.
🔋 Voltage (V)
Definition: The electrical "pressure" that pushes electrons around the circuit. Provided by the dry cell.

Water pipe analogy: Voltage = the pump pressure.

Unit: Volt (V)

Effect: More cells → higher voltage → more current → brighter lamp.
🌊 Interactive Water-Pipe Analogy
Tap a mode to see voltage and current compared.
🔵 Watch Electrons Flow — Toggle the switch
Switch open — electrons don't move
⚠ Common Mistakes — Don't fall for these!
✗ "The battery creates electrons."
✓ The battery gives energy to electrons already in the wire. Electrons exist in all conductors — the cell just pushes them.
✗ "The lamp uses up the current."
✓ Current flows in a complete loop — same current in and out of the lamp. The lamp converts energy (voltage), not current.
Concept Check
A student adds a second dry cell. The lamp becomes brighter. The best explanation is:
AThe current decreased, giving the lamp more energy
BHigher voltage pushes more current → lamp gets more energy per second
CThe lamp created more electrons from the extra cell
DThe resistance of the lamp decreased automatically
E4 · Practice

Apply What You Know

Six questions covering all topics from this lab. No hints — think it through!

Question 1 · Generator vs Receiver
In an electric circuit, a motor is classified as a:
AGenerator — it produces electrical energy
BReceiver — it converts electrical energy into mechanical energy
CInsulator — it prevents current from flowing
DSwitch — it controls the circuit
Question 2 · Conductors
Which of the following is the best conductor of electricity?
ADry wood
BRubber glove
CCopper wire
DGlass rod
Question 3 · Switch State
A lamp in a circuit does NOT light up even though the battery is working. The most likely reason is:
AThe lamp is too bright
BThe switch is open (circuit is broken)
CThere are too many cells
DThe lamp has too many filaments
Question 4 · Too Many Cells
A student connects 4 dry cells to a lamp designed for 1 cell. What most likely happens?
AThe lamp glows at normal brightness
BThe lamp glows weakly because of too much resistance
CThe lamp burns out due to excessive voltage
DNothing happens — the extra cells have no effect
Question 5 · Circuit Symbol
In a circuit diagram, two parallel lines — one longer and one shorter — represent:
AA switch (open)
BA lamp
CA connecting wire
DOne cell (dry cell / battery)
Question 6 · Open Question · AI Tutor 🤖
Explain in your own words: Why does a connecting wire need to be a conductor, and why is it coated with an insulator (like rubber)?
Think about both the inside and outside of a wire.
E5 · Submit

Submit Your Work

Enter your name and class, then submit your answers to Ahmad's grade sheet.

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