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Electricity Circuits

🎓 Class 7 Science CBSE Theory Ch 3 — Electricity: Circuits and Their Components ⏱ ~8 min
🌐 Language: [gtranslate]

This MCQ module is based on: Electricity Circuits

[myaischool_lt_science_assessment grade_level="class_7" science_domain="physics" difficulty="basic"]

📘 Chapter 3 Summary

  • Electricity is used every day for cooking, lighting, transport, heating/cooling, entertainment and communication.
  • A dry cell is a small portable source of electricity with a metal cap (+) and zinc case (−).
  • An electric bulb has a thin tungsten filament inside a sealed glass bulb and two terminals at its base. A fused bulb has a broken filament.
  • An electric circuit is a closed loop along which current flows: cell → wire → bulb → wire → cell.
  • An LED has a long leg (+) and a short leg (−); it works only with correct polarity.
  • A switch opens or closes the circuit to turn a device OFF or ON.
  • Standard symbols are used to draw circuit diagrams quickly and unambiguously.
  • A battery is formed by joining two or more cells (+ of one to − of next) in series.
  • Conductors (metals, graphite, tap water) allow current to flow; insulators (wood, plastic, rubber, glass) do not.
  • Safety first: never touch electric switches with wet hands, never insert objects into sockets, and always use ISI-marked appliances.

🔑 Keywords

Electric CellPortable source of electrical energy (e.g. dry cell, 1.5 V).
BatteryTwo or more cells connected in series.
Electric BulbDevice that lights up when current passes through its filament.
FilamentThin tungsten wire inside the bulb that glows.
Fused BulbBulb with a broken filament — does not glow.
Electric CircuitClosed path along which current flows.
Open CircuitBroken path; no current flows.
Closed CircuitComplete path; current flows.
SwitchDevice to open or close a circuit.
LEDLight Emitting Diode — efficient light source.
ConductorMaterial that allows current (e.g. copper, iron).
InsulatorMaterial that blocks current (e.g. wood, plastic).
TerminalEnd point of a cell or component where wires connect.
CurrentFlow of electricity through a conductor.

📝 NCERT Exercises

Q1Nihal and his classmates listed many uses of electricity. Group the following into broad categories: kettle, tube light, metro train, refrigerator, TV, mobile phone, mixer, fan, AC, lift, radio, internet router, oven, LED lamp.

Cooking: kettle, mixer, oven
Lighting: tube light, LED lamp
Transport: metro train, lift
Heating / Cooling: refrigerator, fan, AC
Entertainment: TV, radio
Communication: mobile phone, internet router.

Q2Name the parts of an electric cell and state their roles.

Metal cap (top): acts as the positive (+) terminal.
Zinc case (body): acts as the negative (−) terminal.
Outer jacket: carries the printed label (brand, voltage, safety info) and insulates the sides.
Inside the cell, chemicals react to produce electricity, which comes out through the two terminals when the cell is connected in a circuit.

Q3In Figure 3.17 two bulbs are connected to a cell through two switches. If the filament of one lamp is broken, will the other still glow? Explain.

L1 (fused) L2 Filament broken
Fig. 3.17: Two bulbs connected in series with one cell.
No, the other bulb will not glow. In a series circuit there is only one path for current. If the filament of L1 is broken, the loop is broken at that point. Current cannot reach L2 either, so both bulbs stay dark.

Q4A student forgot to remove the plastic insulator from the ends of the wires while making a circuit. The bulb and cell are both working fine. Why doesn't the lamp glow?

The plastic coating on a wire is an insulator. If the plastic is not stripped from the ends, the metal inside never touches the cell or bulb terminals. The circuit therefore remains open — no current flows, and the bulb does not glow. Removing about 1 cm of plastic at each end solves the problem.

Q5Draw the circuit diagram of a simple torch using standard symbols (two cells, a switch, and a bulb).

Battery (2 cells) Bulb Switch
Fig. Ex-5: Simple torch circuit with 2-cell battery, bulb and switch.

Q6In Figure 3.18, bulbs L1 and L2 are each controlled by a separate switch (S1 for L1, S2 for L2) in a circuit with one battery. For each case, state which lamp(s) will glow: (a) S1 closed, S2 closed (b) S1 open, S2 closed (c) S1 closed, S2 open (d) S1 open, S2 open.

Battery S1 L1 S2 L2
Fig. 3.18: Two lamps, each with its own switch.
Each lamp sits in its own independent branch controlled by its own switch.
(a) S1 closed, S2 closed: Both L1 and L2 glow.
(b) S1 open, S2 closed: Only L2 glows.
(c) S1 closed, S2 open: Only L1 glows.
(d) S1 open, S2 open: Neither lamp glows.

Q7Vidyut made a circuit like the one shown in Fig 3.19 (cell + switch + bulb). Even after closing the switch, the bulb does not glow. List four possible reasons.

Possible reasons:
  1. The cell is discharged (old/used up) and no longer supplies current.
  2. The bulb is fused — the filament is broken.
  3. The plastic insulation has not been removed from the ends of the wires, so metal is not touching metal.
  4. There is a loose connection at one of the joints, or the switch is not actually closing the contacts.
Other possibilities: cells inserted in wrong direction, or broken wire inside the insulation.

Q8What would happen to your torch if both of its cells are placed in the wrong (reversed) direction? Explain.

If both cells are reversed together, the two + terminals still meet the two − terminals of the bulb and circuit as before — just with polarity flipped. For an ordinary bulb this does not matter, so the bulb still glows. However, if the torch also uses an LED or any polarity-sensitive electronic part, that component will not work because current now flows in the wrong direction. If only one cell is reversed, the two cells oppose each other and the torch will not glow at all.

Q9Give three examples each of conductors and insulators.

Conductors: copper wire, iron nail, aluminium foil (also silver, graphite, tap water).
Insulators: wood, plastic, rubber (also glass, dry paper, porcelain).

Q10Explain why we should never touch electric switches with wet hands.

Ordinary water contains dissolved salts and minerals, which make it a good conductor of electricity. When our hands are wet and we touch a switch, this moisture forms an easy path for current to travel from the live wires into our body. The resulting electric shock can cause serious injury or even be fatal. We must always dry our hands fully before operating any electric switch, plug, or appliance.

Q11Draw the symbols of: (a) an open switch, (b) a battery of 2 cells, (c) a bulb, (d) an LED.

(a) Open switch (b) Battery (2 cells) (c) Bulb (d) LED

Q12A student combines 4 cells of 1.5 V each in series to make a battery. (a) What is the total voltage? (b) Will a 3 V bulb glow safely in this circuit? Justify.

(a) Total voltage = 4 × 1.5 V = 6 V.
(b) No, it is not safe. A 3 V bulb is designed for about 3 V. Connecting it to a 6 V battery will send too much current through the filament, making it get too hot and fuse quickly (burn out). A 6 V bulb (or two 3 V bulbs in series) should be used instead.

Frequently Asked Questions — Electricity Circuits — Chapter 3 Exercises

What does the topic 'Electricity Circuits — Chapter 3 Exercises' cover in Class 7 Science?

The topic 'Electricity Circuits — Chapter 3 Exercises' is part of NCERT Class 7 Science Chapter 3 — Electricity: Circuits and their Components. It covers the key ideas of circuits, conductors, insulators, symbols, NCERT exercises, MCQ, short answer, explained through everyday examples, labelled diagrams and hands-on activities drawn from the NCERT Curiosity textbook. Students learn not just definitions but also the reasoning behind each concept so they can answer competency-based questions and assertion–reason items. The lesson helps Class 7 students build a strong base for higher classes by linking each idea to real observations at home, school and in nature, and by preparing them for CBSE school assessments and Olympiads.

Why is 'Electricity Circuits — Chapter 3 Exercises' important for Class 7 NCERT Science?

'Electricity Circuits — Chapter 3 Exercises' is important because it builds core scientific thinking that Class 7 students will use throughout middle and secondary school. NCERT Chapter 3 — Electricity: Circuits and their Components — introduces circuits and related ideas that appear again in Class 8, 9 and 10 Science. Mastering this subtopic helps students read labels and safety signs, understand news about science and technology, and perform better in CBSE school exams. The chapter also encourages curiosity and evidence-based thinking — skills that support the National Education Policy (NEP) 2020 focus on conceptual understanding and competency-based learning.

What are the key concepts students should remember from Electricity Circuits — Chapter 3 Exercises?

The key concepts in 'Electricity Circuits — Chapter 3 Exercises' for Class 7 Science are: circuits, conductors, insulators, symbols, NCERT exercises, MCQ, short answer. Students should be able to define each term in their own words, give at least one everyday example, and explain how the concept connects to other chapters in NCERT Class 7 Science. For example, linking the idea to daily life — in the kitchen, classroom or outdoors — makes revision easier. Writing short notes, drawing labelled diagrams and solving the NCERT in-text and exercise questions for Chapter 3 will help students retain these concepts for unit tests and the annual CBSE examination.

How is Electricity Circuits — Chapter 3 Exercises taught using activities in NCERT Curiosity Class 7?

NCERT Curiosity Class 7 Science teaches 'Electricity Circuits — Chapter 3 Exercises' using an inquiry-based approach with Predict–Observe–Explain activities. Students are asked to make a guess first, then perform a simple experiment with safe, easily available materials, and finally explain what they observed. This matches the NEP 2020 focus on learning by doing. For Chapter 3 — Electricity: Circuits and their Components — the textbook includes hands-on tasks, labelled diagrams and questions that build Bloom's Taxonomy skills from Remember (L1) to Create (L6). Teachers use these activities, along with competency-based questions (CBQs) and assertion–reason items, to check real understanding rather than rote memorisation.

How should Class 7 students prepare for the Chapter 3 exercises?

To prepare for the Chapter 3 — Electricity: Circuits and their Components — exercises in NCERT Class 7 Science, students should first revise the theory in Parts 1–3 and make a short list of definitions and diagrams for circuits, conductors, insulators, symbols, NCERT exercises, MCQ, short answer. Next, attempt each exercise question on their own before checking the solution. Pay extra attention to MCQs, assertion–reason questions and short-answer items, as these appear in CBSE competency-based tests. Practising with the NCERT Curiosity textbook, the exemplar questions, and the MyAiSchool practice bank helps Class 7 students score better in unit tests and the annual examination.

How does 'Electricity Circuits — Chapter 3 Exercises' connect to other chapters of Class 7 Science?

'Electricity Circuits — Chapter 3 Exercises' connects to many other chapters in NCERT Class 7 Science Curiosity. The ideas of circuits appear again when students study related topics like heat, light, changes, life processes and Earth-Sun-Moon. For example, understanding this subtopic helps in building mental models for later chapters and for Class 8, 9 and 10 Science. Teachers often use cross-chapter questions in CBSE examinations to test whether students can apply what they learned in Chapter 3 — Electricity: Circuits and their Components — to new situations. This integrated approach matches the NEP 2020 and NCF 2023 focus on holistic, competency-based learning.

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