CBSE Class 7 Science Revision Notes Chapter 3: Electricity – Circuits and their Components

An electrical circuit must provide a complete path for current to flow from one terminal of a cell to the other.

Cells, lamps, LEDs, switches and wires work together to control the flow of electric current.

Electricity powers lights, fans, refrigerators, mobile phones, trains, water pumps and many other devices. It can be generated through falling water, wind, sunlight, coal and natural gas. However, simple school experiments use electric cells because household electricity can be extremely dangerous.

These notes follow the current 2026–27 chapter. Revise electric cells, batteries, incandescent lamps, LEDs, switches, complete circuits, circuit diagrams, conductors and insulators. The chapter also explains why a lamp may fail to glow and how electrical materials are selected for safety.

Key Takeaways

• Electric cell: It is a portable source of electrical energy with positive and negative terminals.
• Complete circuit: Current flows only when there is an unbroken path between both cell terminals.
• LED: It glows only when connected in the correct direction.
• Conductors and insulators: Metals conduct current, while materials such as plastic and rubber resist its flow.

Access Class 7 Science Chapter 3 Electricity Circuits Notes in 30 Minutes

Revise the chapter in three parts:

First 10 minutes: Electric cells, batteries, incandescent lamps and LEDs

Next 10 minutes: Complete circuits, switches and circuit diagrams

Final 10 minutes: Conductors, insulators, safety and circuit faults

Need help revising electrical circuits and their components?

Access interactive practice, chapter-wise notes and doubt-solving support on the Extramarks Learning App. Sign Up Free

Uses and Sources of Electricity

Electricity is used in almost every part of modern life.

Its uses can be grouped according to the work performed.

Major Uses of Electricity

Electricity allows machines to perform work faster and makes several daily activities more convenient.

Sources of Electricity

Electricity can be generated using:

• Falling water
• Wind energy
• Solar energy
• Coal
• Natural gas
• Other energy sources

Electricity from power stations reaches buildings through wires.

For classroom activities, students should use only small electric cells or batteries.

Important Safety Rule

Never conduct experiments using:

• Wall sockets
• Household electrical supply
• Portable generators
• Open electrical wires
• Damaged appliances

The current from household supply can cause severe injury or death.

Torchlight and Its Components in Class 7 Science Chapter 3 Notes

A torchlight is a simple device that helps explain how an electrical circuit works.

It usually contains a source, a lamp, conducting parts and a switch.

Main Parts of a Torch

A torch may contain:

• One or more electric cells
• A battery compartment
• An incandescent lamp or LED
• A switch
• Metal contacts
• Connecting wires or strips
• A reflector
• A transparent cover

How Does a Torch Work?

When the switch is moved to the ON position, it completes the circuit.

Current flows from the battery through the lamp and returns to the other battery terminal.

The lamp then glows.

When the switch is moved to the OFF position, a gap appears in the circuit.

Current stops flowing, so the lamp does not glow.

Electric Cell and Battery Revision Notes

Electric cells supply electrical energy to small portable devices.

They are used in torches, wall clocks, remote controls, toys and radios.

What Is an Electric Cell?

An electric cell is a portable source of electrical energy.

Every electric cell has two terminals:

• Positive terminal
• Negative terminal

Terminals of a Cylindrical Cell

A common cylindrical cell has:

• A raised metal cap at one end
• A flat metal disc at the other end

The raised cap is the positive terminal.

The flat disc is the negative terminal.

The symbols marked on the cell are:

• Positive: +
• Negative: −

What Is a Battery?

A combination of two or more cells connected together is called a battery.

The positive terminal of one cell is connected to the negative terminal of the next cell.

This arrangement allows the cells to work together.

Correct Cell Arrangement

In a battery:

Positive terminal of first cell → Negative terminal of second cell

If a cell is reversed incorrectly, the device may not work.

Battery compartments usually show + and − signs to guide correct placement.

Why Are Several Cells Used?

More than one cell may provide:

• Electrical energy for a longer time
• More energy to operate a device
• The required energy for an LED or motor

The exact effect depends on the device and circuit.

Cell and Battery Comparison

In everyday language, people may also call a single cell a battery.

Incandescent Lamp and LED in Electricity Notes

A torch may use an incandescent lamp or an LED.

Both produce light, but their structure and connection rules differ.

Incandescent Lamp

An incandescent lamp contains a thin wire inside a glass bulb.

This thin wire is called a filament.

Main Parts of an Incandescent Lamp

It contains:

• Glass bulb
• Filament
• Two thick supporting wires
• Metal case
• Metal tip
• Insulating material

The filament is connected to two thicker wires.

One thick wire connects to the metal case.

The other connects to the metal tip at the base.

The metal case and metal tip form the two terminals of the lamp.

How Does It Produce Light?

When electric current passes through the filament, it becomes hot.

The hot filament glows and produces light.

Does Connection Direction Matter?

For an incandescent lamp, either terminal may be connected to the positive terminal of the cell.

It will glow as long as:

• Both lamp terminals are connected
• Both cell terminals are connected
• The circuit is complete
• The filament is unbroken

Fused Lamp

An incandescent lamp is called fused when its filament breaks.

The broken filament creates a gap.

Current cannot pass through this gap, so the lamp does not glow.

LED Lamp

LED stands for Light Emitting Diode.

Many modern torches use LEDs instead of incandescent lamps.

Structure of an LED

An LED:

• Has no filament
• Has two wire terminals
• Usually has one longer lead
• Usually has one shorter lead
• Allows current to pass in only one direction

LED Terminals

The longer wire is the positive terminal.

The shorter wire is the negative terminal.

Correct LED Connection

For an LED to glow:

• Its longer positive wire must connect to the positive terminal of the battery.
• Its shorter negative wire must connect to the negative terminal of the battery.

If these connections are reversed, the LED does not glow.

Why Does an LED Work in One Direction?

An LED allows current to pass through it in only one direction.

Therefore, correct polarity is essential.

Incandescent Lamp and LED Comparison

Simple Electrical Circuit

A lamp glows only when its two terminals are connected properly to the two terminals of an electric cell.

This arrangement creates a complete electrical path.

What Is an Electrical Circuit?

An electrical circuit is a complete path through which electric current can flow.

A basic circuit may contain:

• Electric cell
• Connecting wires
• Lamp
• Switch

Correct Connection of a Lamp

To make a lamp glow:

1. Connect one terminal of the cell to one terminal of the lamp.
2. Connect the other lamp terminal to the other cell terminal.
3. Make sure all connections are firm.
4. Check that there is no gap in the path.

The path should begin at one cell terminal, pass through the lamp and return to the other cell terminal.

Direction of Electric Current

The conventional direction of electric current is taken as:

Positive terminal → Circuit components → Negative terminal

This direction is used when drawing and explaining circuits.

Why Does a Lamp Need Two Connections?

Current needs both an outgoing and a returning path.

Connecting only one lamp terminal leaves the circuit incomplete.

The lamp cannot glow in an incomplete path.

Open and Closed Circuits

Electrical circuits are commonly described as open or closed.

The difference depends on whether the path is complete.

Closed Circuit

A closed circuit has a complete and unbroken path.

Current can flow through it.

In a closed circuit:

• The switch is ON.
• Conducting parts touch properly.
• The lamp or LED can glow.
• There is no gap in the path.

Open Circuit

An open circuit contains a gap.

Current cannot flow through it.

In an open circuit:

• The switch is OFF.
• A wire may be disconnected.
• A filament may be broken.
• A terminal may not be touching.
• The lamp does not glow.

Open and Closed Circuit Comparison

A complete circuit may still fail if the cell, lamp or LED is damaged.

Electric Switch in Class 7 Science Chapter 3 Revision Notes

A switch controls whether a circuit remains complete or broken.

It allows a device to be turned ON or OFF.

What Is an Electric Switch?

A switch is a device that completes or breaks an electrical circuit.

It does not produce electric current.

The electric cell or battery is the source of electrical energy.

ON Position

In the ON position:

• The switch contacts touch.
• The gap closes.
• The circuit becomes complete.
• Current flows.
• The lamp glows.

OFF Position

In the OFF position:

• The switch contacts do not touch.
• A gap remains.
• The circuit is open.
• Current does not flow.
• The lamp remains off.

Making a Simple Switch

A basic classroom switch can be made using:

• Two drawing pins
• Safety pin or paper clip
• Piece of cardboard
• Two wires

The safety pin acts as a movable conducting link.

When it touches both drawing pins, the circuit closes.

When it moves away, the circuit opens.

Can a Switch Be Placed Anywhere?

Yes.

A switch can be placed at different positions in a simple circuit.

It controls current by opening or closing the same complete path.

Circuit Symbols and Circuit Diagrams

Actual circuit components can be difficult to draw repeatedly.

Standard symbols make circuit drawings simpler and clearer.

What Is a Circuit Diagram?

A representation of an electrical circuit using standard symbols is called a circuit diagram.

Circuit diagrams show:

• Circuit components
• Connections
• Switch position
• Directional components such as LEDs
• Whether the path is complete

Common Circuit Symbols

Cell Symbol

In the symbol for an electric cell:

• The long line represents the positive terminal.
• The short line represents the negative terminal.

Battery Symbol

A battery symbol contains more than one pair of long and short lines.

It represents two or more connected cells.

LED Symbol

The LED symbol shows the direction in which current can pass.

The outward arrows show that it emits light.

Why Are Standard Symbols Used?

Standard symbols:

• Make diagrams easier to draw
• Reduce confusion
• Save space
• Help people in different countries understand circuits
• Show complex circuits clearly

International organisations develop and standardise many circuit symbols.

Conductors and Insulators

Different materials behave differently when included in an electrical circuit.

Some allow current to pass, while others resist its flow.

What Is a Conduction Tester?

A conduction tester is a simple circuit used to test whether a material allows electric current to pass.

It contains:

• Electric cell
• Lamp
• Connecting wires
• Two free wire ends

The material to be tested is placed between the two free ends.

How to Test a Material

1. Connect a cell and lamp.
2. Keep two wire ends free.
3. First touch the free ends together.
4. Confirm that the lamp glows.
5. Place the test material between the free ends.
6. Observe the lamp.
7. Classify the material.

Conductor

A material through which electric current can flow easily is called a conductor of electricity.

Examples include:

• Copper
• Aluminium
• Iron
• Silver
• Gold
• Metal keys
• Coins
• Steel pins
• Pencil lead

Most metals are conductors.

Insulator

A material through which current does not pass easily is called an insulator or poor conductor.

Examples include:

• Plastic
• Rubber
• Glass
• Ceramics
• Dry wood
• Paper
• Cardboard
• Wax
• Cork

Conductor and Insulator Test Table

Why Is Copper Used in Wires?

Copper is a good conductor of electricity.

It is also more affordable and commonly available than silver or gold.

Therefore, copper is widely used for electrical wiring.

Why Are Wires Covered with Plastic?

The metal inside carries electric current.

The plastic or rubber covering prevents direct contact with the conductor.

This helps protect people from electric shock.

Both Conductors and Insulators Are Useful

Conductors are used in:

• Wires
• Plugs
• Switch contacts
• Socket connectors
• Electrical terminals

Insulators are used in:

• Wire coverings
• Plug tops
• Switch cases
• Tool handles
• Appliance covers

Safe electrical devices use both types of materials.

Electrical Safety

Electricity is useful, but careless handling can be dangerous.

The human body can conduct electric current.

Basic Safety Rules

• Never touch an open wire.
• Never use damaged electrical cords.
• Never touch switches with wet hands.
• Never operate appliances in wet areas.
• Never insert objects into sockets.
• Do not open electrical appliances.
• Stay away from electric poles and transformers.
• Follow danger signs.
• Use cells only for school circuit activities.
• Inform an adult about damaged plugs or insulation.

Why Are Wet Hands Dangerous?

Water on the skin can make it easier for electric current to pass through the body.

This increases the risk of electric shock.

Battery Electricity and Household Electricity

Cells and batteries usually power small devices and provide direct current.

Household electricity comes from power stations and is alternating current.

Household current is much more dangerous and should never be used for student experiments.

Direct Current and Alternating Current

Electric current may be classified according to its direction.

Direct Current

Electricity from cells and batteries is called direct current, or DC.

In DC, the current moves in one direction.

Examples include:

• Torch cells
• Mobile phone batteries
• Laptop batteries
• Rechargeable batteries

Alternating Current

Electricity supplied to wall sockets is called alternating current, or AC.

Its direction changes repeatedly.

It powers:

• Fans
• Refrigerators
• Televisions
• Air conditioners
• Washing machines
• Large appliances

Students only need the basic difference at this level.

Why a Lamp or LED May Not Glow

A non-glowing lamp does not always mean the whole idea of the circuit is wrong.

Several faults are possible.

Common Reasons

• The circuit is open.
• A wire is disconnected.
• The wire ends still have insulating covering.
• The cell is exhausted.
• The cells are arranged incorrectly.
• One cell is reversed.
• The incandescent lamp is fused.
• The LED is connected backwards.
• The LED requires more than one cell.
• The switch is OFF.
• The metal contacts are loose.
• Rust or dirt prevents proper contact.
• Two terminals of the same component are not connected correctly.
• An insulator is placed in the current path.

Step-by-Step Troubleshooting

1. Check whether the switch is ON.
2. Check that all wires are connected.
3. Remove insulation from wire ends.
4. Check cell direction.
5. Test the cell with a known working lamp.
6. Test the lamp with a known working cell.
7. Check whether the filament is broken.
8. Reverse the LED connection if needed.
9. Check whether the LED requires two cells.
10. Tighten loose contacts.
11. Replace any insulator accidentally used as a connector.

Testing one component at a time helps locate the fault.

How to Identify a Working Cell

A simple circuit can test whether a cell is working.

Materials Required

• Small working lamp or LED
• Connecting wires
• Cell holder
• Cells to be tested

Method

1. Make a complete circuit using one test cell.
2. Use a known working lamp.
3. Close the circuit.
4. Observe whether the lamp glows.
5. Repeat with each cell.

A glowing lamp indicates that the cell is supplying electrical energy.

For an LED, ensure correct connection direction.

How to Identify Battery Terminals When Signs Are Missing

An LED can help identify unknown battery terminals.

Method

1. Connect the longer LED lead to one battery terminal.
2. Connect the shorter lead to the other terminal.
3. Observe the LED.
4. If it does not glow, reverse the connections.
5. When it glows, the terminal connected to the longer LED lead is positive.
6. The terminal connected to the shorter lead is negative.

Use only a suitable small battery and LED under teacher supervision.

Electric Cell, Battery, Lamp and LED Comparison

Common Battery Types and Uses

Cells and batteries are made in different sizes and shapes.

Different devices require different types.

Portable batteries make many electrical devices convenient to use.

Class 7 Science Chapter 3 Summary Notes

Important Terms from Electricity: Circuits and their Components

Electricity: A form of energy used to operate lights, machines and devices.

Electric cell: A portable source of electrical energy.

Terminal: A point through which a component connects to a circuit.

Positive terminal: The terminal marked with a plus sign.

Negative terminal: The terminal marked with a minus sign.

Battery: A combination of two or more cells.

Filament: A thin wire inside an incandescent lamp that glows when heated.

LED: A Light Emitting Diode that allows current to pass in one direction.

Electrical circuit: A complete path for electric current.

Electric current: Flow of electricity through a circuit.

Open circuit: An incomplete circuit with a gap.

Closed circuit: A complete circuit through which current can flow.

Switch: A device that completes or breaks a circuit.

Circuit diagram: Representation of a circuit using symbols.

Conductor: A material that allows current to pass easily.

Insulator: A material that does not allow current to pass easily.

Direct current: Electric current flowing in one direction.

Alternating current: Electric current whose direction changes repeatedly.

Useful Links for Class 7 Science