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Notes Chapter 3 Class 7 Science Curiosity NCERT

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Electricity: Circuits and their Components


1. Uses of Electricity

Electricity powers

1. cooking (e.g., microwave),

2.lighting (e.g., bulbs),

3.transportation (e.g., trains),

4. heating/cooling (e.g., AC),

5.entertainment (e.g., TV),

6.communication (e.g., phone),

7. and others (e.g., computer).

Grouping: By location (home, school), function (daily needs, fun), or device type (portable, fixed).


2. Torchlight and Its Components

  • A torchlight uses batteries to produce light via a lamp and switch.

Components:

  • Electric Cell: Portable power source with positive (+) and negative (-) terminals.
  • Battery: 2+ cells connected (+ to -) for more power.
  • Incandescent Lamp: Has a filament that glows when heated.
  • LED Lamp: No filament; glows when current flows correctly (longer wire = positive, shorter = negative).
  • Switch: Completes or breaks the circuit to turn the lamp on/off.

3. Electrical Circuit

  • A complete path for electric current to flow from the positive to negative terminal of a cell through a device (e.g., lamp).
  • Current flows only in a closed circuit. An open circuit (e.g., switch off) stops the flow.
  • Direction: Current flows from positive to negative.

4. Circuit Diagrams

  • Use symbols to represent components (e.g., cell, lamp, switch, wire).
  • Makes circuits easy to draw and understand.
  • Key symbols: Cell (long line = +, short = -), LED (triangle with arrows), switch (line or gap).

5. Conductors and Insulators

  • Conductors: Allow current to flow (e.g., metals like copper, aluminium).
  • Insulators: Do not allow current to flow (e.g., plastic, rubber, wood).
  • Wires are made of conductors (e.g., copper) and covered with insulators (e.g., plastic) for safety.
  • Safety: Our body conducts electricity. Avoid wet hands or damaged devices to prevent shocks.

6. Key Points

  • Cells and batteries power devices portably.
  • Lamps (incandescent/LED) glow when current flows correctly.
  • Switches control circuits (ON = closed, OFF = open).
  • Conductors (metals) and insulators (plastic) are essential for safe circuits.
  • Direct Current (DC): From batteries for small devices.
  • Alternating Current (AC): From wall sockets for large appliances.

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