Class 7 Science Chapter 3 Electricity: Circuits and Their Components notes and book solutions from the NCERT Curiosity textbook with easy explanations, important concepts, examples and complete textbook question answers for revision and exam preparation.

Chapter 3: Electricity: Circuits and their Components

Class 7 Science | Curiosity | Pages 23–40

Chapter Overview

Electricity is an important part of our daily life. We use electricity for lighting, cooking, heating and cooling, communication, entertainment, transportation and many other purposes.

In this chapter, we learn about electric cells, batteries, lamps, LEDs, switches, electrical circuits, circuit diagrams, conductors and insulators.

Important: For school experiments, use only cells or batteries as instructed by your teacher. Do not experiment with electricity from wall sockets.

1. A Torchlight

A torch uses an electric cell or cells, a lamp and a switch. When the switch completes the circuit, electric current can flow and the lamp glows.

Key idea: A torch lamp glows only when there is a complete electrical path through the circuit.

Page 23–24 Question: Can you help Nihal by adding some more uses to his lists?

Solution: More uses include running computers, refrigerators, washing machines, water pumps, fans, televisions and charging electronic devices.

Page 23–24 Question: Also, suggest some other ways of grouping the uses of electricity.

Solution: We can group them as household uses, industrial uses, agricultural uses, transport uses, communication uses and entertainment uses.

Page 24 Question: Why does the torch lamp glow in one position of its switch?

Solution: The lamp glows when the switch completes the circuit. In the other position, the circuit is broken.

2. A Simple Electrical Circuit

An electrical circuit is a complete conducting path through which electric current can flow. A simple circuit can contain a cell, connecting wires, a switch and a lamp.

Simple electrical circuit

2.1 Electric Cell

An electric cell has two terminals. They are marked positive (+) and negative (−). One end has a small protruding metal cap and the other end is generally flat.

Page 25 Question: Do you notice a positive (+ ve) sign and a negative (– ve) sign marked on the electric cell? Do you also notice that it has a small protruding metal cap on one side and a flat metal disc on the other side?

Solution: Yes. The cell has positive and negative terminals. The positive end generally has a protruding metal cap and the negative end is flat.

Page 25 Question: In a torch, we generally use more than one cell. Are those placed in any particular order?

Solution: Yes. Cells are generally arranged so that the positive terminal of one cell touches the negative terminal of the next cell.

2.2 Battery

Two or more cells connected together form a battery. The cells in a battery may be arranged in series or in other arrangements depending on the device.

2.3 Electric Lamp

An incandescent lamp contains a very thin wire called a filament. When electric current passes through the filament, it becomes very hot and glows.

Page 26 Question: Do you notice a thin wire fixed in the middle of the glass bulb?

Solution: Yes. The thin wire is the filament.

Page 26 Question: Now, switch on the torch. Which part of the lamp glows?

Solution: The filament glows.

Page 26 Question: Take out the lamp with the help of your teacher and inspect it from all sides. How is the filament fixed?

Solution: The filament is fixed between the supporting wires inside the bulb.

2.4 LED

An LED is a light-emitting diode. Unlike an incandescent lamp, an LED does not have a filament. An LED has two terminals, and the terminals have different lengths.

Page 27 Question: Take an LED of any colour (Fig. 3.6) and observe. Do you see any filament inside it?

Solution: No. An LED does not have a filament like an incandescent lamp.

Page 27 Question: Notice the length of two wires attached to the LED. Do you find one of those longer than the other?

Solution: Yes. One terminal is longer than the other.

LED correctly connected to a battery with positive and negative terminals

Correct connection of an LED with a battery

Remember: In the arrangement shown above, the longer LED terminal is connected to the positive terminal and the shorter terminal is connected to the negative terminal.

3. Making an Electric Lamp Glow

A lamp glows only when its two terminals are connected properly to the two terminals of a cell or battery through conducting wires and the circuit is complete.

If the circuit is broken at any point, electric current cannot flow and the lamp does not glow.

Page 30 Question: Can you find the reason for the difference?

Solution: The difference occurs because the components are connected differently. A correct connection completes the circuit, while an incorrect connection does not.

Page 30 Question: How will you decide which is the positive terminal of this battery?

Solution: We can identify the positive terminal using a known LED or another suitable test arrangement, while following the correct safety procedure.

4. An Electrical Circuit

A circuit must provide a continuous conducting path from one terminal of the cell through the components and back to the other terminal.

Page 31 Question: Does the LED glow?

Solution: The LED glows when it is connected in the correct direction and the circuit is complete.

Page 31 Question: Does the LED glow again?

Solution: It glows when the LED is connected with the correct polarity.

Page 31 Dive Deeper Question: Sometimes you may come across a device in which the cells are placed side by side. Then, how are the terminals of the cells connected?

Solution: In a side-by-side arrangement, the cells may be connected according to the circuit design so that the required terminals are connected correctly.

5. Electric Switch

A switch is used to complete or break an electrical circuit. When the switch is ON, the circuit is complete and current can flow. When the switch is OFF, the circuit is broken.

Page 32 Question: How does a switch turn on or off the torchlight?

Solution: The switch completes the circuit when ON and breaks the circuit when OFF.

Page 32 Activity Question: Does the lamp glow?

Solution: The lamp glows when the circuit is complete.

Page 32 Activity Question: Does the lamp glow now?

Solution: It does not glow if the switch has broken the circuit.

Simple rule: ON = closed circuit = current can flow = lamp can glow.
OFF = open circuit = current cannot flow = lamp does not glow.

6. Circuit Diagrams

Drawing a real electrical circuit every time can be difficult. Therefore, standard symbols are used to represent electrical components.

Component	Representation
Electric cell	Standard cell symbol
Battery	Combination of cell symbols
Electric lamp	Standard lamp symbol
Switch	Open or closed switch symbol
Connecting wire	Straight line

Page 33 Question: Can we represent the circuits in a simpler manner?

Solution: Yes. We can use standard symbols to draw simple circuit diagrams.

Page 34 Question: Are your circuit diagrams similar to Fig. 3.14a and Fig. 3.14b respectively?

Solution: A correct circuit diagram should use the standard symbols and show the connections clearly.

7. Electrical Conductors and Insulators

Materials through which electric current can pass are called conductors. Metals such as copper, aluminium and iron are generally good conductors.

Materials through which electric current does not pass easily are called insulators. Rubber, plastic, glass and dry wood are examples of insulators.

Page 34 Question: Why did we use metal wires for making electric circuits? Can we not use some other materials for wires?

Solution: Metals are good conductors, so electric current can pass through them easily. Insulating materials would not work well as connecting wires.

Page 34 Question: Also, why are electric wires covered with plastic or rubber?

Solution: Plastic and rubber are insulators. They help protect us from contact with the conducting metal wire.

Page 35 Question: Suppose, we make wires of materials other than metal and use them for making the electrical circuit. Do you think the electric current will pass through those materials in such a circuit?

Solution: It depends on the material. Current passes through conductors but does not pass easily through insulators.

Page 35 Activity Question: Does the lamp glow?

Solution: The lamp glows when the tested material allows current to pass and the circuit is complete.

Page 35 Activity Question: Does the lamp glow every time?

Solution: No. It depends on the material placed in the circuit.

Page 35 Question: Did the lamp glow for all materials?

Solution: No. The lamp glows for conducting materials but not for insulating materials.

Page 36 Question: Have you now understood why wires are covered with those materials?

Solution: Yes. Wires are covered with insulating materials such as plastic or rubber to provide protection from the conducting metal.

Page 36 Dive Deeper Question: Have you ever wondered how the electricity from a cell or battery is different from the electricity coming from a wall socket?

Solution: A cell or battery provides direct current (DC), while electricity supplied through household wall sockets is alternating current (AC).

8. Important Difference: Conductors and Insulators

Conductors	Insulators
Allow electric current to pass through them easily.	Do not allow electric current to pass through them easily.
Copper	Rubber
Aluminium	Plastic
Iron	Glass

9. In a Nutshell

Electricity is used for many purposes in our daily life.
An electric cell has positive and negative terminals.
Two or more cells connected together can form a battery.
An incandescent lamp has a filament that glows when heated by electric current.
An LED does not have an incandescent filament.
An electrical circuit must be complete for current to flow.
A switch is used to complete or break a circuit.
Standard symbols are used for drawing circuit diagrams.
Metals are generally good conductors of electricity.
Plastic, rubber and glass are examples of insulators.
Cell and battery supplies are examples of DC sources, while household socket supply is AC.

10. Let Us Enhance Our Learning

Page 37 — Question 1: Choose the incorrect statement.
(i) A switch is the source of electric current in a circuit.
(ii) A switch helps to complete or break the circuit.
(iii) A switch helps us to use electricity as per our requirement.
(iv) When the switch is in ‘OFF’ position, there is an air gap between its terminals.

Solution: (i) is incorrect. A switch is not the source of electric current.

Page 37 — Question 2: Observe Fig. 3.16. With which material connected between the ends A and B, the lamp will not glow?

Solution: The lamp will not glow when an insulating material, such as rubber or plastic, is connected between A and B.

Page 38 — Question 3: In Fig. 3.17, if the filament of one of the lamps is broken, will the other glow? Justify your answer.

Solution: If the lamps are connected in the same series path, the other lamp will not glow because the broken filament breaks the complete circuit.

Page 38 — Question 4: A student forgot to remove the insulator covering from the connecting wires while making a circuit. If the lamp and the cell are working properly, will the lamp glow?

Solution: No. The insulating covering prevents proper electrical contact.

Page 38 — Question 5: Draw a circuit diagram for a simple torch using symbols for electric components.

Solution: The diagram should contain a cell or battery, a switch, a lamp and connecting wires forming a complete circuit. The switch should be closed for the lamp to glow.

Page 38 — Question 6: In Fig. 3.18:
(i) If S2 is in ‘ON’ position, S1 is in ‘OFF’ position, which lamp(s) will glow?
(ii) If S2 is in ‘OFF’ position, S1 is in ‘ON’ position, which lamp(s) will glow?
(iii) If S1 and S2 both are in ‘ON’ position, which lamp(s) will glow?
(iv) If both S1 and S2 are in ‘OFF’ position, which lamp(s) will glow?

Solution: The exact lamp names depend on the connections shown in Fig. 3.18. The rule is simple: a lamp glows only when there is a complete conducting path from the cell or battery through that lamp.

Page 38 — Question 7: Vidyut has made the circuit as shown in Fig. 3.19. Even after closing the circuit, the lamp does not glow. What can be the possible reasons? List as many possible reasons as you can for this faulty operation. What will you do to find out why the lamp did not glow?

Solution: Possible reasons include:

The cell may be exhausted.
The lamp may be fused.
A wire may be loose.
The wires may not be making proper contact.
The switch may not be working properly.
The circuit may not actually be complete.
The connections may be incorrect.

Check each component and connection one by one using a known working component.

Page 39 — Question 8: In Fig. 3.20, in which case(s) the lamp/LED will not glow when the switch is closed?

Solution: The lamp or LED will not glow in any arrangement where the circuit is incomplete or the LED is connected with incorrect polarity.

Page 39 — Question 9: Suppose the ‘+’ and ‘–’ symbols cannot be read on a battery. Suggest a method to identify the two terminals of this battery.

Solution: Connect a known LED in a simple circuit. The terminal of the battery connected to the longer LED terminal when the LED glows is the positive terminal.

Page 39 — Question 10: You are given six cells marked A, B, C, D, E, and F. Some of these are working and some are not. Design an activity to identify which of them are working.
(i) List the items that you require.
(ii) Write the procedure that you will follow.
(iii) With the items, carry out the activity to identify the cells that are working.

Solution:(i) Items required: A small lamp or suitable LED, connecting wires and a suitable holder.

(ii) Procedure: Connect each cell separately to the lamp or LED using connecting wires. Make sure the connections are complete.

(iii) Observation: If the lamp glows or the LED glows correctly, the cell is working. If it does not glow with proper connections, the cell may not be working.

Page 39 — Question 11: Using an LED that requires two cells in series to glow, Tanya made the circuit as shown in Fig. 3.21. Will the lamp glow? If not, draw the wires for correct connections.

Solution: The LED will glow only when both cells are connected in the correct series direction and the LED polarity is correct. If the cells or LED are connected incorrectly, the circuit must be rewired so that the required positive and negative terminals are connected correctly.

11. Exploratory Projects

Project 1

Suppose the power supply is disrupted for two days. Make a list of the daily activities that you would not be able to do easily.

Project 2

Use a solar panel as a source of electricity and make a simple circuit to run a toy fan.

Project 3

Visit a shop selling electrical items. Identify different types of cells and the devices in which they are used. Prepare a short report.

Project 4

Prepare a list of objects found at home under three categories: insulators only, conductors only and objects that may contain both conducting and insulating materials.

12. Science and Society

Electricity has transformed modern life. It supports communication, transportation, education, healthcare, industries, homes and many other areas. At the same time, electricity must be used carefully because unsafe handling can cause electric shocks, burns and fires.

Safety Rule: Never experiment with wall-socket electricity. School experiments should use cells or batteries under proper supervision.

Quick Revision

Term	Easy Meaning
Electric cell	A source of electrical energy with positive and negative terminals.
Battery	Two or more cells connected together.
Electric lamp	A device that produces light when current passes through it.
LED	Light-emitting diode that produces light when correctly connected.
Switch	A device used to complete or break a circuit.
Electrical circuit	A complete conducting path through which current can flow.
Conductor	A material that allows electric current to pass through it easily.
Insulator	A material that does not allow electric current to pass through it easily.
DC	Direct current, supplied by cells and batteries.
AC	Alternating current, supplied through household wall sockets.

“`0

Prepare for your exams with this easy and student-friendly Class 7 Science Chapter 3 worksheet. Practice the questions carefully to revise important concepts, strengthen your understanding, and improve your Science skills.

🔬

CLASS 7 • SCIENCE

Class 7 Science Chapter 3 Worksheet

Practice worksheet for Class 7 Science Chapter 3 with important questions, extra practice and answer key.

Start Worksheet

Class 7 Science Chapter 3 NotesClass 7 Science Chapter 3 SolutionsElectricity Circuits and Their Components Class 7 NotesElectricity Circuits and Their Components Class 7 SolutionsClass 7 Science Curiosity NotesClass 7 Science Curiosity Chapter 3 SolutionsNCERT Class 7 Science Chapter 3 SolutionsClass 7 Science Book SolutionsClass 7 Science Chapter 3 Question AnswersClass 7 Curiosity Science Notes

Class 7 Science Chapter 3 Electricity Circuits and Their Components Notes & Solutions | Curiosity