CBSE Class 6 Science Ch 12: Electricity & Circuits

Chapter 12: Electricity and Circuits

This chapter introduces the basic concepts of electricity, its sources, and how it flows through simple circuits. It covers essential components like electric cells, bulbs, and switches, as well as the important distinction between conductors and insulators.

Chapter Summary

• Electric Current: The flow of electric charge is called electric current. We use electricity in our daily lives for lighting, heating, and running appliances.
• Electric Cell: An electric cell is a source of electricity. It converts chemical energy into electrical energy.
  • It has two terminals: a positive (+) terminal and a negative (-) terminal.
  • The metal cap is usually the positive terminal, and the metal disc is the negative terminal.
• Electric Bulb: An electric bulb has a thin wire called a filament. The filament glows when an electric current passes through it.
  • The filament is fixed to two thicker wires, which provide support and also connect the filament to the terminals of the bulb.
  • A bulb 'fuses' when its filament breaks, creating a break in the circuit, and thus the current cannot flow.
• Electric Circuit: A complete path for electricity to flow is called an electric circuit.
  • A circuit is closed when the path is complete, allowing current to flow and the bulb to glow.
  • A circuit is open when there is a break in the path, preventing current flow and the bulb from glowing.
• Electric Switch: A simple device that either breaks the circuit (turns off) or completes the circuit (turns on). It makes it convenient to use electricity without connecting and disconnecting wires every time.
• Conductors: Materials that allow electric current to pass through them are called conductors. Most metals like copper, aluminum, and iron are good conductors of electricity. Our body is also a good conductor.
• Insulators: Materials that do not allow electric current to pass through them are called insulators. Examples include plastic, wood, rubber, and air. Insulators are used for safety purposes to cover electrical wires and handles of tools.
• Safety with Electricity: It is dangerous to touch electric wires or switches with wet hands or with bare hands. Always use insulating materials for protection. Never experiment with the electricity supply from the mains, generators, or inverters.
• Battery: When two or more electric cells are joined together, it forms a battery. Often, cells are arranged so that the positive terminal of one cell is connected to the negative terminal of the next cell.

Questions and Answers

1. Fill in the blanks:

(a) A device that is used to break an electric circuit is called a __________.

(b) An electric cell has __________ terminals.

Answer:

(a) A device that is used to break an electric circuit is called a switch.

(b) An electric cell has two terminals.

2. Mark ‘True’ or ‘False’ for following statements:

(a) Electric current can flow through metals.

(b) Instead of metal wires, a jute string can be used to make a circuit.

(c) Electric current can pass through a sheet of thermo Col.

Answer:

(a) True

(b) False

(c) False

3. Explain why the bulb would not glow in the arrangement shown in Fig. 12.13.

(Note: Fig. 12.13 shows an open circuit where one terminal of the bulb is not connected to the cell, or where insulating material is used in the circuit.)

Answer:

The bulb would not glow in the arrangement shown because the circuit is incomplete. In a complete circuit, both terminals of the bulb must be connected to the two terminals of the electric cell. If there is a break in the circuit, or if an insulating material is placed in the path, electric current cannot flow through the filament of the bulb, and thus the bulb will not glow.

4. Complete the drawing shown in Fig 12.14 to indicate where the free ends of the two wires should be joined to make the bulb glow.

(Note: Fig. 12.14 shows an electric cell and a bulb with two free wires from the cell and two free wires from the bulb.)

Answer:

To make the bulb glow, one free end of the wire from the cell should be joined to one terminal of the bulb, and the other free end of the wire from the cell should be joined to the other terminal of the bulb. This completes the circuit, allowing current to flow from the positive terminal of the cell, through the bulb's filament, and back to the negative terminal of the cell.

5. What is the purpose of using an electric switch? Name some electrical gadgets that have switches built into them.

Answer:

The purpose of using an electric switch is to easily make or break an electric circuit. It allows us to turn an electrical appliance on or off without having to connect or disconnect wires manually. Some electrical gadgets that have switches built into them are:

• Torch
• Table lamp / Desk lamp
• Radio
• Television
• Mixer-grinder
• Fan

6. Would the bulb glow in the circuit shown in Fig. 12.15?

(Note: Fig. 12.15 shows a circuit where the two terminals of the bulb are connected to only one terminal of the electric cell.)

Answer:

No, the bulb would not glow in the circuit shown in Fig. 12.15. For a bulb to glow, both terminals of the electric cell must be connected to the two terminals of the bulb to complete the circuit and allow current to flow. Connecting both wires from the bulb to a single terminal of the cell does not complete the circuit.

7. Using the “conduction tester” on an object it was found that the bulb glows. Is that object a conductor or an insulator? Explain.

Answer:

If the bulb glows when using a conduction tester on an object, that object is a conductor. This is because conductors are materials that allow electric current to pass through them, completing the circuit and causing the bulb to light up. Insulators, on the other hand, do not allow current to pass, so the bulb would not glow if an insulator were used.

8. Why should an electrician use rubber gloves while repairing an electric switch at your home? Explain.

Answer:

An electrician should use rubber gloves while repairing an electric switch at home because rubber is an insulator. Insulators do not allow electric current to pass through them. By wearing rubber gloves, the electrician prevents any electric current from flowing through their body, thus protecting them from electric shock. Our body is a good conductor of electricity, so without insulation, there is a risk of a dangerous shock.

9. The handles of the tools like screwdrivers and pliers used by electricians for repair work usually have plastic or rubber covers on them. Can you explain why?

Answer:

The handles of tools like screwdrivers and pliers used by electricians have plastic or rubber covers on them because plastic and rubber are insulators. This means they do not conduct electricity. The metal part of these tools can conduct electricity, so the insulating covers on the handles protect the electrician from electric shock by preventing the flow of current to their hands when they work with live wires or electrical components.