Science · Class 7 · Chapter 3

Electricity: Circuits and their Components

Aim: Build a clear, working understanding of this chapter's key ideas, connected to real NCERT examples, worked problems, and everyday situations.
  • 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.
  • 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.
  • Conductor / Insulator — Lets current through easily / blocks it.
  • DC / AC — Direct current (cells) / alternating current (mains).
40 min lesson

Chapter 3 · Concept 1 of 8

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).

Chapter 3 · Concept 2 of 8

Battery

  • When two or more cells are connected — positive 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.")

Chapter 3 · Concept 3 of 8

Incandescent Lamps and LEDs

  • 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.
  • 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.

Chapter 3 · Concept 4 of 8

Building an Electrical Circuit

  • The lamp glows only when both cell terminals connect through the lamp, forming one complete path — a circuit.

Chapter 3 · Concept 5 of 8

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.

Chapter 3 · Concept 6 of 8

Standard Circuit Symbols

  • A circuit diagram uses standard symbols instead of drawings, so anyone can read it.

Chapter 3 · Concept 7 of 8

Conductors and Insulators

  • Conductors — Let electric current flow easily — mostly metals, like copper (cheap, abundant, used for wires).
  • Insulators — Block current flow — plastic, rubber, ceramics. Wires are covered in these to protect us, since the human body itself conducts electricity.

Chapter 3 · Concept 8 of 8

DC and AC

  • DC — Direct Current — Comes from cells and batteries, typically powering small devices.
  • AC — Alternating Current — Comes from wall sockets and power plants, able to run larger appliances.

Quick Recap

Check Your Understanding

  1. 1Choose 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. 2A 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. 3Draw a circuit diagram for a simple torch, using symbols for its electric components.