A torchlight's lamp glows in only one switch position. What's really happening inside that simple circuit?
Key idea
The Electric Cell
A torchlight has a lamp, a switch, and
inside — two or more electric cells.
Two terminals, always
Every electric cell has a positive terminal (the protruding metal cap) and a negative terminal (the flat metal disc).
Key idea
Battery
When two or more cells are connectedpositive terminal of one touching the negative terminal of the next — the combination is called a battery.
Why connect cells?It powers a circuit for longer, or delivers more energy. (In everyday speech, even a single cell — like in a phone — is often just called its "battery.")
Key idea
Incandescent Lamps and LEDs
1
Incandescent lamp
A thin wire — the filament — heats up and glows. It doesn't matter which of its two terminals connects to which end of the cell.
→
2
LED
Has no filament, just two wires of different lengths — the longer wire is positive, the shorter is negative. Current can only flow through it one way.
Key idea
Building an Electrical Circuit
The lamp glows only when both cell terminals connect through the lamp, forming one complete path — a circuit.
Key idea
The Electric Switch
A switch can be homemade. Two drawing pins, a safety pin, and a piece of cardboard are enough to build a working switch.
Key idea
Standard Circuit Symbols
A circuit diagram uses standard symbols instead of drawings, so anyone can read it.
Key idea
Conductors and Insulators
1
Conductors
Let electric current flow easily — mostly metals, like copper (cheap, abundant, used for wires).
→
2
Insulators
Block current flow — plastic, rubber, ceramics. Wires are covered in these to protect us, since the human body itself conducts electricity.
Key idea
DC and AC
1
DC
Direct Current — Comes from cells and batteries, typically powering small devices.
→
2
AC
Alternating Current — Comes from wall sockets and power plants, able to run larger appliances.
Chapter · Key terms to remember
Key Terms
Electric cell
A source of electrical energy with + and − terminals.
Battery
Two or more cells connected together.
Filament
The thin wire that glows in an incandescent lamp.
Chapter · Key terms to remember
More Key Terms
LED
A lamp that lets current flow in only one direction.
Electrical circuit
A complete path for current to flow.
Circuit diagram
A circuit shown using standard symbols.
Chapter · Key terms to remember
More Key Terms
Conductor / Insulator
Lets current through easily / blocks it.
DC / AC
Direct current (cells) / alternating current (mains).
Questions for your notebook
Write these down, then discuss
1
Choose the incorrect statement: (i) A switch is the source of electric current in a circuit. (ii) A switch helps complete or break a circuit. (iii) A switch lets us use electricity as needed. (iv) When OFF, a switch has an air gap between its terminals.
2
A student forgot to strip the insulation off the connecting wires while building a circuit. If the lamp and cell both work properly, will the lamp glow?
3
Draw a circuit diagram for a simple torch, using symbols for its electric components.
Project as-is — students copy the questions, then the class discusses answers together.