CLASS 7 · SCIENCE · CHAPTER 3

Electricity: Circuits and Their Components

Simple answers to all 11 end questions, chapter activities, and all four exploratory projects.

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Textbook pages 37–39

Question 1

Choose the incorrect statement: (i) A switch is the source of electric current. (ii) A switch completes or breaks a circuit. (iii) A switch helps us use electricity when needed. (iv) An OFF switch has a gap between its terminals.

Steps only

A switch controls the circuit; it is not the source of current.

Answer

(i)

Question 2

With what kind of material placed between A and B will the lamp not glow?

Steps only

Use an insulator such as rubber or plastic.

Answer

An insulator makes the lamp stay off.

Question 3

If the filament of one of the lamps in Figure 3.17 is broken, will the other lamp glow? Explain.

Steps only

No. A broken filament opens the shared circuit path.

Answer

The other lamp will not glow.

Question 4

A student forgot to remove the insulating covering from the connecting wires. If the cell and lamp work, will the lamp glow?

Steps only

No. Insulated wire ends cannot make electrical contact; expose and connect the metal ends.

Answer

The lamp will not glow until the metal wire ends make contact.

Question 5

Draw a circuit diagram for a simple torch using symbols for the electrical components.

Steps only

Battery → switch → lamp → back to battery, all in one loop.

Answer

Draw a battery, switch, and lamp in a single series loop.

Question 6

In Figure 3.18, state which lamps glow when: (i) S2 ON and S1 OFF; (ii) S2 OFF and S1 ON; (iii) both switches ON; (iv) both switches OFF.

Steps only

(i) L2 (ii) L1 (iii) L1 and L2 (iv) neither

Answer

Only lamps on branches with closed switches glow.

Question 7

The circuit is closed but the lamp does not glow. List possible causes and explain how to find the fault.

Steps only

Check the cell, lamp, wire contacts, switch, and LED direction one at a time.

Answer

A dead cell, fused lamp, loose wire, poor contact, or reversed LED may be the cause.

Question 8

In Figure 3.20, identify the cases in which the lamp or LED will not glow when the switch is closed.

Steps only

An LED glows only when its positive side faces the battery’s positive terminal.

Answer

Only (c) will not glow.

Question 9

If the + and − signs cannot be read on a battery, how can you identify its terminals?

Steps only

Use an LED tester: when it glows, battery + is connected to the LED's longer lead.

Answer

The battery end connected to the LED's long lead when it glows is positive.

Question 10

Design a safe activity to find which of six cells A–F are working. List materials and steps.

Steps only

Test A–F one at a time in the same small-battery lamp circuit and record which ones glow.

Answer

A cell that powers the tester is working.

Question 11

Tanya connects an LED that needs two cells in series as shown in Figure 3.21. Will it glow? If not, how should the wires be connected?

Steps only

No, it will not glow: both LED leads connect to positive cell ends. Join one cell's positive end to the other's negative end; connect the free + to the LED's longer lead and free − to its shorter lead.

Answer

No, it will not glow as drawn: both LED leads connect to positive cell ends. Put the cells in series; connect free + to the longer LED lead and free − to the shorter lead.

Chapter activities and learning prompts

Textbook pages 23–36, 39–40

Question Opening activity

Add examples of electricity use under the chapter headings and suggest another way to group them.

Steps only

Electricity powers lights, speakers, cookers, pumps, lifts, and communication devices.

Answer

Group uses by task or by the output they produce.

Question Activities 3.1–3.7

What are the two terminals of a cell? How must an incandescent lamp and an LED be connected to glow?

Steps only

Cell: + and −. Incandescent lamp: complete path. LED: long lead to +, short lead to −.

Answer

A complete circuit is needed; an LED also needs correct polarity.

Question Activity 3.11

Which common materials conduct electricity, and why are wires covered with plastic or rubber?

Steps only

Metals conduct. Plastic and rubber insulate and cover wires for safety.

Answer

Metal carries current; the insulating covering helps protect us.

Question Activity 3.8

How can you make a simple switch using a safety pin or paper clip, drawing pins, cardboard, and wires?

Steps only

Two pins are the contacts; a movable metal clip joins or separates them.

Answer

Touch both pins with the clip to close the switch; lift it to open it.

Question Activity 3.9

What happens to the lamp when the switch contacts touch? What happens when there is a gap?

Steps only

Touching contacts complete the path; a gap breaks it.

Answer

Closed: lamp glows. Open: lamp stays off.

Question Activity 3.10

Draw circuit diagrams for the circuits shown in Figures 3.12(a) and 3.10(c), using symbols instead of pictures.

Steps only

Use component symbols, preserve the connections, and show the correct switch position and LED direction.

Answer

Draw the same circuits with standard symbols and the same connections.

Exploratory Projects

Textbook pages 39–40

Question Exploratory project

Which daily activities might be affected if electricity were unavailable for two days?

Steps only

Lighting, cooling, charging, internet, pumps, refrigerators, and electric cooking may be affected.

Answer

List the electrical services you depend on and safe alternatives.

Question Project 2

How can a solar panel be used to make a toy fan run?

Steps only

Connect a correctly rated solar panel to a toy fan, then compare its motion in sunlight and shade.

Answer

The solar panel converts light energy into electrical energy for the fan.

Question Project 3

What types of electric cells are sold nearby, and which devices use each type? Prepare a short report.

Steps only

Ask an adult to help you survey a shop; record each cell type and the devices that use it.

Answer

Report the cell types actually found and their common uses.

Question Project 4

List household objects that are insulators, conductors, or made of both kinds of material.

Steps only

Examples: rubber eraser—insulator; metal spoon—conductor; insulated wire—both.

Answer

Sort everyday objects by the materials in each object.