Hinglish

Circuit Diagrams

Class 7 Science · Chapter 3: Electricity: Circuits and their Components · NCERT Curiosity section 3.3

Learn

Drawing real cells, lamps and wires is slow. Instead we use symbols. A cell is a long line (+) and a short line (−); a battery is two or more cells in a row; a lamp is a circle with a cross; a wire is a straight line.

An LED is a triangle with a bar, plus two little arrows for the light it gives out; the triangle points the way current can flow. A switch is a lever between two dots: closed (ON) or tilted open (OFF).

A drawing of a circuit made with symbols is a circuit diagram. Here is a torch: a battery, a switch and a lamp in one loop. With the switch ON the lamp glows. Anyone in the world can read it, because organisations agree on standard symbols.

Reading diagrams helps find faults. If a lamp will not glow, check: is every switch ON? Is there a gap or loose wire? Is an LED the wrong way round? Is a filament broken? Is the cell used up? Zoya tests one thing at a time.

Explore: close the circuit.

  1. Turn on what is needed to make the lamp glow.

Remember

  • A circuit diagram shows a circuit with standard symbols.
  • Cell: long line +, short line −. LED: the triangle points the way current flows.

Quick check

In a cell symbol, which line is the positive terminal?

  1. the longer line
  2. the shorter line
  3. both
  4. neither
Answer

the longer line. Long line +, short line −.

Think about it

A lamp will not glow even after the switch is closed. List possible reasons and how you would check each.

One answer

Used-up cell (try it in another circuit), broken filament (look at the lamp or swap it), loose or unstripped wire ends (check the joints), a cell the wrong way in a battery, or a faulty switch (bypass it with a wire).

Practice

Practise with fresh questions at three levels (easy, medium, hard), some answered hands-on, with hints and worked answers. Get 4 of your last 5 right to finish the topic.