12. Electricity and Circuits

Introduction: Imagine life without electricity! No fans, no lights, no TV. We use electricity for many purposes to make our tasks easier. For example, lifting water from wells using pumps.

Electric Cell

The source of electricity in a torch is the electric cell. Cells are also used in clocks, radios, and cameras.

Positive Terminal (+): The metal cap side.
Negative Terminal (-): The metal disc side.

How it works: An electric cell produces electricity from the chemicals stored inside it. When chemicals are used up, the cell stops working.

Warning:

Never connect the two terminals of a cell directly with a wire. The chemicals will get used up very fast and the cell will stop working.

Electric Bulb and Circuit

Bulb: Contains a thin wire called Filament that glows when current passes through it. The filament is fixed to two thick wires.

Electric Circuit: A complete path for electricity to pass (current to flow) between the two terminals of the electric cell. Current flows from Positive (+) to Negative (-).

Closed Circuit: Complete path. Bulb glows.
Open Circuit: Broken path (wire broken or switch off). Bulb does not glow.
Fused Bulb: If the filament is broken, the circuit is incomplete, so it won't glow.

ACTIVITY 2: Simple Circuit

Experiment: Connect a wire from + terminal of cell to one terminal of bulb. Connect another wire from - terminal of cell to other terminal of bulb. The bulb glows!

Electric Switch

A simple device that either breaks the circuit or completes it. When the switch is ON, the circuit is complete. When OFF, the circuit is broken.

Conductors and Insulators

Conductors: Materials which allow electric current to pass through them. (Examples: Copper, Aluminum, Iron, Graphite, Human Body, Water).
Insulators: Materials which do not allow electric current to pass through them. (Examples: Rubber, Plastic, Wood, Glass, Air).

ACTIVITY 5: Conduction Tester

Test: Replace a part of the wire in a circuit with different materials.

Key (Metal): Bulb glows -> Conductor.
Eraser (Rubber): Bulb does not glow -> Insulator.
Scale (Plastic): Bulb does not glow -> Insulator.

Safety First!

Your body is a conductor of electricity. Therefore, be careful when you handle electrical appliances. Electricians wear rubber gloves (insulators) to protect themselves.

Chapter Summary

Electric cell is a source of electricity.
An electric cell has two terminals; one is called positive (+ ve) while the other is negative (– ve).
An electric bulb has a filament that is connected to its terminals.
An electric bulb glows when electric current passes through it.
In a closed electric circuit, the electric current passes from one terminal of the electric cell to the other terminal.
Switch is a simple device that is used to either break the electric circuit or to complete it.
Materials that allow electric current to pass through them are called conductors.
Materials that do not allow electric current to pass through them are called insulators.

Exercise Q1: Fill in the blanks

A device that is used to break an electric circuit is called a Switch.
An electric cell has Two terminals.

Exercise Q2: True or False

Electric current can flow through metals. (True)
Instead of metal wires, a jute string can be used to make a circuit. (False)
Electric current can pass through a sheet of thermocol. (False)

Exercise Q3

Q: Explain why the bulb would not glow in an arrangement where a screwdriver with a plastic handle is used to connect wires?

Ans: The handle of a screwdriver is made of plastic or rubber, which is an insulator. Insulators do not allow electric current to pass through them. Thus, the circuit is broken, and the bulb does not glow.

Exercise Q5

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

Ans: A switch is a simple device used to either break the electric circuit or complete it. It allows us to turn an appliance ON or OFF easily. Examples: Torch, Radio, TV, Fan, Washing Machine.

Exercise Q6

Q: Would the bulb glow if a safety pin connects the two wires in a circuit instead of a switch?

Ans: Yes. A safety pin is made of metal (steel/iron), which is a conductor. Completed circuit allows current to flow.

Exercise Q8

Q: Using the conduction tester on an object, it was found that the bulb begins to glow. Is that object a conductor or an insulator?

Ans: The object is a Conductor, because it allows electric current to pass through it, completing the circuit and making the bulb glow.

Exercise Q9

Q: Why should an electrician use rubber gloves while repairing an electric switch at your home?

Ans: An electrician touches electric wires which may carry current. Our body is a conductor, so touching a live wire can cause a shock. Rubber gloves are insulators. They prevent the current from flowing from the wire into the electrician's body, protecting them from shock.

Exercise Q10

Q: 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?

Ans: Plastic and rubber are insulators. The covers protect the electrician from electric shock by stopping the flow of current from the tool to their hand.

Key Facts and Definitions

1. Important Definitions

Electricity: A form of energy used to operate many devices like fans, bulbs, etc.
Filament: Thin wire in a bulb that gives off light when heated by electricity.
Switch: Device to complete or break a circuit.
Terminal: The points where connections are made (Positive and Negative).

2. Safety Facts

Never touch electrical switches with wet hands. Water (tap water) is a conductor.
Human body is a conductor of electricity. That's why we get shocks.
Air is an insulator. If it were a conductor, electricity would flow through air and shock us without wires!

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