Chapter 3: Electricity: Circuits and their ComponentsClass 7 Science — summary, notes, extra questions & NCERT solutions

Summary

Starting from a familiar torchlight, this chapter builds an understanding of simple electrical circuits and their components. An electric cell is a portable source of electrical energy with two terminals — a positive (+) metal cap and a negative (-) metal disc. Connecting two or more cells so that the positive terminal of one touches the negative terminal of the next forms a battery, which can supply energy for longer or in greater amount. Two kinds of lamps are studied: the incandescent lamp, whose thin filament gets hot and glows when current passes, and the LED (Light Emitting Diode), which has no filament and lets current pass in one direction only — its longer wire is positive and shorter wire is negative. A lamp glows only when its two terminals are joined to the two terminals of the cell so that there is a complete path for current; this path is an electrical circuit. By convention, current flows from the positive to the negative terminal of the cell. A switch is a simple device that completes (ON, closed circuit) or breaks (OFF, open circuit) the path. Circuits can be drawn compactly using standard symbols for cells, batteries, lamps, LEDs, switches, and wires, giving a circuit diagram. The chapter then classifies materials: good conductors (mostly metals such as copper, silver, and gold) let current flow easily, while insulators or poor conductors (plastic, rubber, glass, ceramics) do not — which is why wires are made of metal but covered with plastic or rubber for safety.

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