Class 6 Science Notes Chapter 12 (Chapter 12) – Examplar Problem Book

Detailed Notes with MCQs of Chapter 12: Electricity and Circuits from your Science Exemplar book. This is a fundamental chapter, and understanding these concepts well is crucial, not just for your class exams but also for various government competitive exams where basic science is tested. 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 converts chemical energy stored inside it into electrical energy. It provides the electricity needed to make devices like bulbs glow or toys run.
• Components:
  • Terminals: Every electric cell has two terminals:
    • Positive Terminal (+): Usually marked with a '+' sign; often the metal cap on top.
    • Negative Terminal (-): Usually marked with a '-' sign; often the flat metal base (disc).
  • Chemicals: Contains chemicals that react to produce electricity. Once these chemicals are used up, the cell stops producing electricity and needs replacement.
• Function: Provides a potential difference (voltage) that pushes electric current through a circuit.

2. Electric Bulb: Using Electricity

• Function: A device that converts electrical energy into light energy (and some heat energy).
• Components:
  • Filament: A very thin wire inside the glass bulb, usually made of Tungsten. When electric current passes through it, it gets heated to a high temperature and starts glowing.
  • Terminals: A bulb also has two terminals for connection:
    • One terminal is the metal casing at the base (often threaded).
    • The other terminal is the metal tip at the center of the base.
  • Glass Casing: Protects the delicate filament. Often filled with an inert gas.
• Fused Bulb: If the filament inside the bulb breaks, the path for the current is broken, and the bulb will not glow. This is called a 'fused' bulb.

3. Electric Circuit: The Path for Current

• Definition: An electric circuit is the complete and continuous path along which electric current can flow.
• Components of a Simple Circuit:
  • Source of electricity (e.g., an electric cell)
  • Device that uses electricity (e.g., a bulb)
  • Connecting wires (usually made of metal like copper, covered with plastic insulation)
  • Optional: A switch
• Flow of Current: Conventionally, the direction of electric current is taken from the positive (+) terminal of the cell, through the bulb and wires, back to the negative (-) terminal of the cell.
• Requirement for Current Flow: The circuit must be closed and unbroken.

4. Open and Closed Circuits

• Closed Circuit:
  • A complete path exists from one terminal of the cell, through the bulb and switch (if ON), back to the other terminal.
  • Current flows through the circuit.
  • The bulb glows (if connected correctly and not fused).
• Open Circuit:
  • There is a break in the path (e.g., a loose connection, broken wire, fused filament, or the switch is OFF).
  • Current cannot flow through the circuit.
  • The bulb does not glow.

5. Electric Switch: Controlling the Circuit

• Definition: A simple device used to either complete (close) or break (open) an electric circuit easily.
• Function: It acts as a controller for the flow of current.
  • 'ON' Position: The switch completes the circuit (closes it). Current flows.
  • 'OFF' Position: The switch breaks the circuit (opens it). Current stops flowing.
• Construction: Switches are made using conducting materials for the connection points and insulating materials for the parts we touch. Common household switches work on this principle.

6. 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 (the lead in pencils), tap water (due to dissolved salts), human body.
  • Uses: Making electric wires, terminals, filaments, switch contacts.
• Insulators:
  • Definition: Materials that do not allow electric current to pass through them easily (or at all).
  • Reason: Their electrons are tightly bound and cannot move freely.
  • Examples: Plastic, rubber, wood, glass, air, pure water, paper, cloth, porcelain.
  • Uses: Covering electric wires (insulation), making switch casings, handles of electrical tools (like screwdrivers) for safety.

7. Safety Precautions with Electricity

• Never touch electrical wires or appliances with wet hands (water, especially impure water, is a conductor).
• Never experiment with the electric supply from the mains or generators – it is very high voltage and dangerous. Only use electric cells for experiments.
• Ensure proper insulation on wires and handles of tools.
• Replace damaged wires or plugs immediately.
• Understand the importance of insulators for safety.

Key Takeaways for Exams:

• Know the definition and function of each component: Cell, Bulb, Wire, Switch.
• Be able to identify the terminals of a cell and a bulb.
• Understand the difference between an open and a closed circuit and its effect on the bulb.
• Be able to classify common materials as conductors or insulators.
• Know the reason why conductors conduct and insulators insulate (basic idea of electron movement).
• Remember safety rules related to electricity.
• Be able to draw or interpret simple circuit diagrams.

Multiple Choice Questions (MCQs)

Here are 10 MCQs based on Chapter 12 to test your understanding:

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 light energy
   (b) Chemical energy into electrical energy
   (c) Electrical energy into chemical energy
   (d) Light energy into electrical energy

3. For an electric current to flow, the circuit must be:
   (a) Open
   (b) Broken
   (c) Closed
   (d) Made of insulators only

4. Which of the following materials is an electrical insulator?
   (a) Copper wire
   (b) Aluminium foil
   (c) Rubber band
   (d) Iron nail

5. A device used to easily open or close an electric circuit is called a/an:
   (a) Bulb
   (b) Cell
   (c) Wire
   (d) Switch

6. How many terminals does a standard electric cell have?
   (a) One
   (b) Two
   (c) Three
   (d) Four

7. In a simple circuit with a cell, bulb, and wires, the bulb does not glow. Which of these could be a reason?
   (a) The circuit is closed.
   (b) The filament of the bulb is broken.
   (c) The cell is new.
   (d) The wires are made of copper.

8. The handles of tools like screwdrivers and pliers used by electricians are usually covered with:
   (a) Aluminium
   (b) Copper
   (c) Iron
   (d) Plastic or Rubber

9. Which of the following is necessary for a bulb connected to a cell to glow?
   (a) The switch must be in the 'OFF' position.
   (b) The filament must be broken.
   (c) There must be a complete path from one terminal of the cell, through the bulb, back to the other terminal.
   (d) The wires must be covered with rubber.

10. Which statement is correct regarding electric current?
    (a) It can flow through an open circuit.
    (b) Insulators allow it to pass easily.
    (c) It flows from the negative to the positive terminal inside the cell (conventionally considered outside).
    (d) It requires a source like an electric cell to flow in a circuit.

Answer Key for MCQs:

1. (c) Filament
2. (b) Chemical energy into electrical energy
3. (c) Closed
4. (c) Rubber band
5. (d) Switch
6. (b) Two
7. (b) The filament of the bulb is broken.
8. (d) Plastic or Rubber
9. (c) There must be a complete path from one terminal of the cell, through the bulb, back to the other terminal.
10. (d) It requires a source like an electric cell to flow in a circuit.

Study these notes thoroughly. Remember, understanding the 'why' behind each concept is as important as knowing the definition itself. Good luck with your preparation!