Electricity: Circuits & Components | Science Grade 7 CBSE

Play with it

What completes the circuit?

The cell, bulb and wires are ready — but there's a gap. Put different things in it and see when the bulb lights. A closed loop through a conductor glows; an open gap or an insulator stays dark.

Explore · Build the circuittap a material

Open gap — the circuit is broken, so the bulb is off.

Learn

The three big ideas

An electric cell pushes current around a loop. It has two terminals — positive (+) and negative (−). A circuit is the path the current takes: cell → wire → bulb → wire → back to the cell.

Closed circuit — the loop is complete, current flows, the bulb glows.
Open circuit — there's a break (a gap, a switch turned off), so no current flows.
A switch is simply a controllable gap: closing it completes the loop, opening it breaks it.
Joining two or more cells (+ to −) makes a battery, which gives a bigger push.

Put something into the gap of a circuit and you can test it:

Conductors let current pass — most metals (copper, aluminium, iron), and a few non-metals like graphite (pencil lead). The bulb glows.
Insulators block current — plastic, rubber, glass, dry wood, air. The bulb stays off.

That's why wires are copper inside, plastic outside: copper carries the current, the plastic keeps it from reaching your hand.

Safety first: only ever experiment with cells and batteries. Never use the electricity from a wall socket (mains) — it is far stronger and can give a dangerous, even fatal, shock.

Inside a bulb is a thin coiled wire — the filament. When current passes through it, it heats up so much that it glows and gives light. This is the heating effect of electric current.

Scientists draw circuits with simple symbols (a long-and-short line for a cell, a circle with a cross for a bulb, a gap with a lever for a switch) so any circuit can be sketched quickly and clearly.

Worked example. In the explorer above, the switch is closed and a copper wire fills the gap, yet the bulb still doesn't glow. Name two simple things that could be wrong.

1) A loose connection somewhere — even a tiny break opens the loop.

2) The bulb's filament is fused (broken) — so the loop is open inside the bulb itself.

Both are "open circuit" problems: the current has no complete path.

Where you'll meet it

Circuits you use every day

A torch

Cell + bulb + switch + a metal strip — exactly the loop above. Slide the switch and you close the circuit; the filament glows. Flat batteries can't push enough current, so the light dims.

Why plugs and tools have plastic

The handle of a screwdriver, the body of a plug, the coating on a wire — all insulators, placed exactly where your hand goes, so the current stays on its copper path and not through you.

Check yourself

Competency quiz

Modelled on the competency-based pattern — MCQ, assertion–reason and a case study, testing whether you can use the idea, not just recall it.

Score 0/12

Electricity:Circuits & Components