Class 6 Science Notes Chapter 12 (Electricity and Circuits) – Science Book

Alright class, let's get straight into Chapter 12: Electricity and Circuits. This is a fundamental chapter, and understanding these basics is crucial, not just for your exams but also for everyday safety and knowledge. Pay close attention!

Chapter 12: Electricity and Circuits - Detailed Notes for Exam Preparation

1. Electric Cell: The Source of Electricity

• Definition: An electric cell is a device that produces electricity from chemical energy stored inside it. It acts as a portable source of electric current.
• Terminals: Every electric cell has two terminals:
  • Positive Terminal (+): Usually marked with a '+' sign; often has a metal cap.
  • Negative Terminal (-): Usually marked with a '-' sign; often has a flat metal base.
• Function: The chemical reactions inside the cell generate a potential difference (voltage) between the terminals, causing electric current to flow when connected in a complete circuit.
• Current Flow: In a circuit connected to a cell, the electric current flows from the positive terminal to the negative terminal outside the cell.
• Usage: Used in torches, clocks, remote controls, toys, etc.
• Caution: Once the chemicals are used up, the cell stops producing electricity and needs replacement (or recharging if it's a rechargeable cell, though primary cells discussed here are typically non-rechargeable).

2. Electric Bulb: How it Glows

• Structure: An electric bulb consists of:
  • Filament: A very thin wire (usually made of tungsten) inside the glass bulb. This is the part that heats up and glows.
  • Terminals: A bulb also has two terminals for connection:
    • One terminal is the metal casing at the base (around the screw threads or sides).
    • The other terminal is the metal tip at the centre of the base.
  • Glass Casing: Protects the filament and often contains an inert gas or vacuum.
• Working Principle: When electric current passes through the filament, it gets heated to a very high temperature and starts glowing, producing light.
• Fused Bulb: A bulb is said to be 'fused' when its filament is broken. A broken filament means an incomplete path, so current cannot flow, and the bulb will not glow.

3. Electric Circuit: The Path for Electricity

• Definition: An electric circuit is a complete and continuous path through which electric current can flow.
• Components: A simple circuit typically includes:
  • A source of electricity (e.g., an electric cell).
  • Connecting wires (usually made of metal like copper, covered with insulation).
  • An electrical appliance (e.g., a bulb).
  • Optionally, a switch.
• Types of Circuits:
  • Closed Circuit: An unbroken path from one terminal of the electric cell, through the wires and bulb (or other device), back to the other terminal of the cell. Current flows, and the bulb glows.
  • Open Circuit: A broken or incomplete path. There is a gap somewhere in the circuit (e.g., a loose connection, broken wire, open switch, fused bulb). Current cannot flow, and the bulb does not glow.
• Direction of Current: As mentioned, conventionally, the direction of current flow is taken from the positive (+) terminal to the negative (-) terminal of the cell in the external circuit.

4. Electric Switch: Making and Breaking the Circuit

• Definition: An electric switch is a simple device used to either complete ('close' or 'ON') or break ('open' or 'OFF') an electric circuit.
• Function: It provides a convenient way to control the flow of current without disconnecting wires.
• Working:
  • ON Position: The switch connects the two points in the circuit, completing the path for current flow.
  • OFF Position: The switch creates a gap, breaking the circuit and stopping the current flow.
• Simple Switch: Can be made using safety pins, paper clips, and drawing pins on a base material (like thermocol or wood), demonstrating the principle of making or breaking contact.

5. Conductors and Insulators: Materials and Electricity

• Conductors:
  • Definition: Materials that allow electric current to pass through them easily.
  • Reason: They have free electrons that can move and carry charge.
  • Examples: All metals (copper, aluminum, iron, silver, gold), graphite (pencil lead), tap water (due to dissolved salts), human body.
  • Uses: Making electric wires, terminals, filaments.
• Insulators:
  • Definition: Materials that do not allow electric current to pass through them easily.
  • Reason: Their electrons are tightly bound and cannot move freely.
  • Examples: Rubber, plastic, glass, wood (dry), air, pure water, porcelain, paper, cloth.
  • Uses: Covering electric wires (for safety), making switch casings, handles of electrical tools (like screwdrivers).

6. Electrical Safety

• Importance: Electricity can be dangerous if not handled properly.
• Key Points:
  • Our body is a conductor of electricity. Touching live wires or faulty appliances can cause severe electric shock.
  • Never experiment with electricity from the mains supply (wall sockets) or generators. Use only electric cells for experiments.
  • Ensure wires are properly insulated. Do not use wires with damaged insulation.
  • Water increases conductivity. Avoid handling electrical appliances with wet hands or in wet areas.
  • Use switches and plugs made of insulating materials.

Key Takeaways for Exams:

• Know the definitions of cell, bulb, circuit (open/closed), switch, conductor, insulator.
• Be able to identify the terminals of a cell and a bulb.
• Understand the condition required for a bulb to glow (closed circuit, intact filament).
• Be able to classify common materials as conductors or insulators.
• Remember the basic safety precautions related to electricity.
• Understand the function of each component in a simple circuit.

Multiple Choice Questions (MCQs)

1. Which part of an electric bulb glows when current passes through it?
   a) Glass casing
   b) Metal base

   • c) Filament
     d) Terminals

2. An electric cell converts:
   a) Electrical energy into chemical energy

   • b) Chemical energy into electrical energy
     c) Light energy into electrical energy
     d) Electrical energy into heat energy

3. Which of the following is necessary for a bulb to glow in a simple circuit?
   a) An open circuit

   • b) A closed circuit
     c) A fused bulb
     d) A switch in the OFF position

4. Which of these materials is an electrical insulator?
   a) Copper wire
   b) Aluminum foil
   c) Graphite

   • d) Rubber band

5. A device used to easily open or close an electric circuit is called a:
   a) Cell
   b) Bulb

   • c) Switch
     d) Filament

6. An electric cell has how many terminals?
   a) One

   • b) Two
     c) Three
     d) Four

7. In a circuit diagram, the direction of current flow is conventionally shown from:
   a) Negative terminal to positive terminal of the cell

   • b) Positive terminal to negative terminal of the cell
     c) The bulb to the cell
     d) The switch to the bulb

8. What happens when the filament of a bulb breaks?
   a) The circuit remains closed
   b) The bulb glows brighter

   • c) The circuit becomes open, and the bulb does not glow
     d) The cell stops working

9. Why are handles of tools like screwdrivers and pliers used by electricians usually covered with plastic or rubber?
   a) To make them look attractive
   b) To make them easier to hold

   • c) Because plastic/rubber are insulators and protect from electric shock
     d) Because plastic/rubber are good conductors of heat

10. Which of the following materials is a good conductor of electricity?
    a) Dry wood
    b) Glass

    • c) Tap water
      d) Air

Make sure you revise these notes thoroughly. Understanding the 'why' behind each concept is as important as remembering the definitions. Good luck with your preparation!