Class-7 | Chapter 3: Electricity: Circuits and their Component | Science

 

Electricity

Electricity is a form of energy that helps us operate many devices and machines in our daily life. It is produced from sources like power stations, batteries, and solar cells.

Electricity flows through a closed path called an electric circuit.

Uses of Electricity

Electricity is very important in homes, schools, hospitals, industries, and transportation.

1. Domestic Uses

Electricity is used in homes for:

• Lighting bulbs and tubes
• Running fans and coolers
• Operating televisions, refrigerators, and washing machines

2. Communication

Electricity helps in communication devices such as:

• Mobile phones
• Computers
• Internet systems

3. Transportation

Electricity is used in:

• Electric trains
• Metro systems
• Electric vehicles

4. Medical Uses

Hospitals use electricity for:

• X-ray machines
• Ventilators
• Medical equipment

5. Industrial Uses

Factories use electricity to run:

• Machines
• Motors
• Production equipment

6. Agricultural Uses

Electricity is used for:

• Water pumps
• Irrigation systems
• Agricultural machines

Importance of Electricity:

• Makes work easier and faster
• Saves time and effort
• Improves quality of life
• Helps in scientific and technological development

Safety Measures While Using Electricity:

1. Do not touch switches with wet hands.
2. Avoid damaged wires.
3. Switch off appliances when not in use.
4. Keep electrical devices away from water.

Electric Cell

An electric cell is a device that converts chemical energy into electrical energy. It provides electricity to operate electrical devices.

Components of an Electric Cell

An electric cell has:

1. Positive terminal (+)
2. Negative terminal (−)

Electric current flows from the positive terminal to the negative terminal through a circuit.

Uses of Electric Cells

Electric cells are used in:

• Clocks
• Torches
• Remote controls
• Toys

Examples

• Dry cell
• Button cell

Battery:

A battery is an electrical device made up of one or more cells that converts chemical energy into electrical energy. It provides electric current to operate various electronic devices such as mobile phones, torches, clocks, toys, cars, and laptops.

Inside a battery, chemical reactions take place between different substances called electrodes and electrolytes. These reactions produce electric energy, which flows through a circuit and powers devices.

Uses of Batteries

Batteries are used in:

• Mobile phones
• Flashlights
• Watches
• Remote controls
• Electric vehicles
• Computers and laptops

Electric Lamps

Electric lamps are devices that convert electrical energy into light energy. They are commonly used for lighting homes, schools, offices, and streets.

Types of Electric Lamps

1. Incandescent Lamp

An incandescent lamp produces light by heating a thin tungsten filament inside a glass bulb. When electric current passes through the filament, it becomes very hot and glows, producing light.

Features

• Gives yellowish light
• Produces more heat
• Consumes more electricity
• Less energy efficient

Uses

• Older household lighting
• Decorative lighting

2. LED Lamp

LED stands for Light Emitting Diode. It produces light when electric current passes through a semiconductor material.

Features

• Very energy efficient
• Produces less heat
• Long lifespan
• Brighter and more durable

Uses

• Home lighting
• Street lights
• Mobile screens
• TVs and electronic devices

Constructing Circuits

A circuit is a closed path through which electric current flows. Constructing a circuit means connecting electrical components properly so that electricity can flow and operate devices.

Basic Components of a Simple Circuit

1. Electric Cell or Battery – Supplies electrical energy.
2. Connecting Wires – Carry electric current.
3. Switch – Opens or closes the circuit.
4. Bulb or LED – Uses electricity to produce light.

Steps to Construct a Simple Circuit

1. Take a battery, bulb, switch, and wires.
2. Connect one terminal of the battery to the switch using a wire.
3. Connect the switch to the bulb.
4. Connect the other side of the bulb back to the other terminal of the battery.
5. Close the switch to complete the circuit.

When the switch is closed, current flows and the bulb glows.

Open and Closed Circuits

• Closed Circuit – The path is complete, so current flows.
• Open Circuit – The path is broken, so current does not flow.

Switches and Their Role

A switch is an electrical device used to open or close an electric circuit. It controls the flow of electric current in a circuit.

Role of a Switch

• Closing the switch completes the circuit and allows current to flow.
• Opening the switch breaks the circuit and stops the flow of current.

Because of this, a switch helps us turn electrical devices ON and OFF safely and easily.

Types of Switches

1. Manual Switch – Operated by hand
   Example: Light switch
2. Automatic Switch – Works automatically under certain conditions
   Example: Electric bell switch

Importance of Switches

• Provide safety
• Save electricity
• Control electrical devices conveniently

Conductors and Insulators

Materials are classified as conductors or insulators based on their ability to allow electric current to pass through them.

Conductors

Conductors are materials that allow electric current to flow easily through them because they have free electrons.

Examples

• Copper
• Aluminium
• Iron
• Silver

Uses

• Electric wires
• Electrical appliances
• Circuits

Copper and aluminium are commonly used in electrical wiring because they are good conductors of electricity.

Insulators

Insulators are materials that do not allow electric current to pass through them easily.

Examples

• Rubber
• Plastic
• Wood
• Glass

Uses

• Covering electric wires
• Safety equipment
• Handles of electrical tools

Insulators protect us from electric shocks by preventing the flow of electricity.

Important Safety Precautions

1. Do not touch electrical appliances with wet hands
   Water conducts electricity and may cause electric shock.
2. Do not touch bare wires
   Exposed wires can be dangerous and may cause serious injury.
3. Use insulated wires and tools
   Rubber or plastic covering protects from electric shocks.
4. Switch off appliances when not in use
   This saves electricity and prevents accidents.
5. Do not overload electric sockets
   Too many devices on one socket may cause overheating or fire.
6. Keep electrical devices away from water
   Water can damage appliances and increase the risk of shock.
7. Turn off the main power supply before repairing electrical equipment
   This helps prevent accidents.
8. Report damaged wires or switches immediately
   Faulty equipment should be repaired by an electrician.

Importance of Electrical Safety

• Prevents electric shocks
• Reduces fire hazards
• Protects electrical appliances
• Ensures safe use of electricity

Electric Current

Electric current is the flow of electric charges (usually electrons) through a conductor such as a wire.

It is measured in ampere (A) using an instrument called an ammeter.

Definition

“Electric current is the rate of flow of electric charges through a conductor.”

Types of Electric Current

1. Direct Current (DC)

In direct current, electric charges flow in only one direction.

Features

• Flows in a single direction
• Produced by cells and batteries
• Commonly used in electronic devices

Examples

• Mobile phone batteries
• Power banks

2. Alternating Current (AC)

In alternating current, the direction of current changes repeatedly after fixed intervals of time.

Features

• Changes direction continuously
• Supplied to homes and industries
• Can travel long distances efficiently

Examples

• Household electricity
• Fans