Chapter 3: Electricity — Circuits and their Components
Cells • Batteries • Lamps (Filament & LED) • Switches • Circuit Diagrams • Conductors & Insulators
🔋 Power • 🔗 Circuit • 💡 Glow • 🛡️ Safety
🗝️20 Most-Important Words (Meanings in Simple Hindi)
| Word | Meaning (Hindi) |
|---|---|
| Electricity | ऊर्जा का रूप जो तारों/उपकरणों से होकर बहता है और काम कराता है। |
| Electric cell | छोटा, पोर्टेबल स्रोत जो बिजली देता है (जैसे रिमोट/टॉर्च में)। |
| Positive terminal (+) | सेल का वह सिरा जहाँ से परंपरागत धारा शुरू मानी जाती है; “+” चिन्ह। |
| Negative terminal (–) | सेल का दूसरा सिरा; “–” चिन्ह से दिखाया जाता है। |
| Battery | दो या अधिक सेल मिलाकर बना स्रोत (अधिक/लंबे समय तक ऊर्जा देता है)। |
| Incandescent lamp | बल्ब जिसमें पतला तार (फिलामेंट) गरम होकर चमकता है। |
| Filament | बल्ब के अंदर पतला तार जो गरम होकर प्रकाश देता है। |
| LED | लाइट एमिटिंग डायोड; बिना फिलामेंट के, एक दिशा में धारा मिलने पर जलता है। |
| Circuit | पूरा रास्ता जिससे धारा बहकर उपकरण तक जाती है। |
| Electric current | बिजली का प्रवाह; परंपरा से + से – की ओर माना जाता है। |
| Switch | परिपथ को जोड़ने/तोड़ने वाला साधन (ON/OFF)। |
| Open circuit | टूटा हुआ रास्ता; धारा नहीं बहती, बल्ब नहीं जलता। |
| Closed circuit | पूरा रास्ता; धारा बहती है, बल्ब जलता है। |
| Circuit diagram | चिह्नों से बना परिपथ का सरल चित्र। |
| Electrical symbol | घटकों (सेल, बैटरी, स्विच, LED) के मानक चिन्ह। |
| Conductor | ऐसा पदार्थ जिसमें धारा आसानी से बहती है (धातु, तांबा)। |
| Insulator | ऐसा पदार्थ जिसमें धारा नहीं बहती (प्लास्टिक, रबर, काँच)। |
| Direct Current (DC) | बैटरी/सेल से मिलने वाली धारा जो एक ही दिशा में बहती है। |
| Alternating Current (AC) | घर के सॉकेट से मिलने वाली धारा जिसकी दिशा समय-समय पर बदलती है। |
| Fused lamp | बल्ब का फिलामेंट टूट जाने से न जलने की स्थिति। |
📚Detailed Notes — Electricity: Circuits and their Components
🔌Everyday Uses of Electricity
Electricity is everywhere: homes, schools, markets, factories and transport.
- Lighting: homes, offices, streets, markets, factories.
- Cooking: electric kettle, mixer–grinder, toaster, oven, microwave.
- Heating & Cooling: fan, heater, immersion rod, geyser, refrigerator, AC.
- Entertainment: television, radio, music systems.
- Communication: mobile phones, internet devices.
- Transportation & Handling: trains, lifts, escalators, e-vehicles, cranes.
- Others: water pumps, computers, medical devices, lab instruments.
⚡Where Electricity Comes From
- Hydroelectric power: falling water turns turbines (e.g., Bhakra Nangal Dam).
- Wind energy: windmills generate electricity.
- Solar energy: solar panels capture Sun’s energy.
- Thermal plants: using coal/natural gas.
- Delivery: power travels via wires to homes and industries.
Safety First: Never experiment with mains electricity. For classroom experiments use only cells/batteries.
🔦Torchlight Basics
- A torch has a lamp and a switch; sliding the switch closes/opens the circuit.
- Inside are one or more electric cells providing energy to the lamp.
🔋Electric Cell & Battery
- Cell terminals: metal cap = positive (+), metal disc = negative (–).
- Battery: two or more cells connected series ( + of one to – of next ).
- More cells → lamp can glow brighter/for longer (more energy available).
- People often say “battery” even for a single cell (common usage).
💡Incandescent Lamp (Bulb)
- Has a thin filament fixed to two thicker support wires inside a glass bulb.
- Two terminals at base: metal tip and metal case (kept insulated from each other).
- When current flows through the filament, it gets hot and glows.
- Fused lamp: if filament breaks, current stops and bulb will not glow.
🔶LED (Light Emitting Diode)
- No filament; gives light when current passes in the correct direction only.
- Terminals: longer lead = positive, shorter lead = negative.
- To glow: connect LED + to battery + and – to battery –.
🔗Making a Lamp/LED Glow — The Circuit
Complete path needed: The lamp glows only when there is a closed circuit from cell’s + to – through the lamp.
- Wiring a cell and lamp: connect one terminal of lamp to one terminal of cell and the other lamp terminal to the other cell terminal.
- Conventional current direction: taken from positive → negative terminal of the cell.
- Incandescent lamp: polarity doesn’t matter; only the circuit must be complete.
- LED: polarity matters; it glows in only one direction.
- Cell/Battery holders & tape: helpful to connect wires firmly to terminals.
- Side-by-side cells: inside many devices, metal strips connect + of one to – of the next (look for printed “+ / –” marks).
🧲Switch — ON/OFF Control
- A switch is a device that completes (ON) or breaks (OFF) a circuit.
- Simple classroom switch: safety pin + two drawing pins on a cardboard.
- Open circuit (OFF): there is a gap; current cannot flow; lamp won’t glow.
- Closed circuit (ON): no gap; current flows; lamp glows.
- Switch can be placed anywhere in series with the lamp and cell.
🧭Circuit Diagrams & Symbols
- We draw circuits using standard symbols to make them easy to read.
- Cell: long line = +, short line = –.
- Battery: series of long–short pairs.
- Lamp (bulb): standard lamp symbol.
- LED: triangle with a bar; triangle points in the allowed current direction; arrows show light.
- Switch: symbols for ON (closed) and OFF (open).
- Standards: IEC, ANSI, IEEE publish common symbol sets used worldwide.
🔧Conductors vs Insulators
- Use a simple tester (cell + lamp + two free wire ends).
- Touch free wire ends to both ends of a material:
- If lamp glows → material is a conductor (e.g., metals: copper, aluminium, keys, foil).
- If lamp does not glow → insulator (e.g., plastic, rubber, wood, glass, cork).
- Wires: made of conductors (mostly copper) for good flow; covered with insulators (plastic/rubber) for safety.
🛡️Safety & Types of Current
- Human body is a conductor. Electric current can cause severe injury or death.
- Never touch switches with wet hands or use damaged plugs/sockets.
- For experiments, use only cells/batteries, never mains supply.
- DC (Direct Current): from cells/batteries; flows one way; powers small devices.
- AC (Alternating Current): from power plants to wall sockets; direction changes periodically; runs larger appliances.
🧠In a Nutshell (Quick Revision)
- An electric cell is a portable energy source with + / – terminals.
- Two or more cells in series form a battery.
- Incandescent lamps have a filament that glows when current flows; a broken filament → fused bulb.
- LEDs light only when connected with correct polarity; current allowed in one direction.
- A switch opens/closes the circuit (OFF/ON).
- Conventional current direction: + → –.
- Circuit diagram uses standard symbols (cell, battery, lamp/LED, switch, wires).
- Conductors let current pass (metals); insulators do not (plastic, rubber, glass).
- DC from cells; AC from mains supply.
Practice Pointers: Be able to (i) identify when a lamp will/won’t glow from a sketch, (ii) draw a simple torch circuit with symbols, (iii) spot wiring mistakes (reversed LED leads, broken filament, open switch, insulation not stripped), (iv) predict which materials will conduct, and (v) trace current direction.
Practice Pack — Electricity: Circuits & Components
One-word • Fill in the Blanks • True/False • Very Short • Short Answers
🔋🔗💡🧭🛡️
🎯Section 1 — One-Word Answers (10)
1) Portable source of electrical energy used in torches:
Cell
2) Two or more cells connected in series form a:
Battery
3) Thin wire inside a bulb that glows:
Filament
4) Device used to open or close a circuit:
Switch
5) A material that allows current to pass easily:
Conductor
6) A material that does not allow current to pass:
Insulator
7) Current supplied by cells/batteries:
DC
8) Current supplied by wall sockets:
AC
9) LED glows only with correct ________:
Polarity
10) Drawing of a circuit using symbols:
Circuit diagram
🧩Section 2 — Fill in the Blanks (10)
| Question | Answer |
|---|---|
| 1) The metal cap of a cell is the ______ terminal. | positive |
| 2) In an incandescent lamp, the ______ gets hot and glows. | filament |
| 3) Conventional current is taken from ______ to ______ terminal. | positive to negative |
| 4) A circuit with a gap is called an ______ circuit. | open |
| 5) A circuit without a gap is a ______ circuit. | closed |
| 6) In a battery, the positive of one cell connects to the ______ of the next. | negative |
| 7) An LED allows current in only one ______. | direction |
| 8) Wires are commonly made of copper because it is a good ______. | conductor |
| 9) Wire insulation is usually made of ______ or rubber. | plastic |
| 10) If the filament breaks, the bulb is said to be ______. | fused |
✅Section 3 — True / False with Explanations (10)
| # | Statement | Answer | Explanation |
|---|---|---|---|
| 1 | A switch is the source of electric current in a circuit. | False | A switch only opens/closes the circuit; the cell/battery is the source. |
| 2 | An incandescent bulb can glow regardless of which terminal is connected to + or –. | True | Polarity doesn’t matter for a filament; only a complete circuit is required. |
| 3 | An LED will glow whichever way it is connected. | False | LEDs are polar devices; they glow only with correct polarity. |
| 4 | Plastic is a good electrical conductor. | False | Plastic is an insulator; it prevents current flow and is used for wire covering. |
| 5 | The metal cap of a dry cell is the negative terminal. | False | The cap is the positive terminal; the flat base is negative. |
| 6 | Conventional current direction is from the negative to the positive terminal. | False | By convention it is from positive to negative terminal of the cell. |
| 7 | A battery always means a single cell. | False | Technically, a battery is two or more cells connected together. |
| 8 | In a closed circuit, the lamp can glow because current flows. | True | No gap exists; charges can move through the lamp filament/LED. |
| 9 | The human body can conduct electricity. | True | The body contains electrolytes; current can pass and cause harm. |
| 10 | Alternating current (AC) is obtained from cells and batteries. | False | Cells provide DC; AC is supplied by power plants via wall sockets. |
✍️Section 4 — Very Short Answers (10) • 2–3 lines each
1) How does a torchlight work?
A torch contains cells (or a battery), a lamp (bulb/LED) and a switch. Sliding the switch closes the circuit so current flows from the cell’s + to – through the lamp, making it glow.
2) How can you identify the terminals of a dry cell?
The small metal cap is the positive (+) terminal and the flat metal disc is the negative (–) terminal. These markings are also printed on the cell.
3) Why might an incandescent bulb fail to glow even in a closed circuit?
Its filament may be broken (“fused”), so current cannot pass through it. A loose connection at the terminals can also prevent current flow.
4) Why are wires covered with plastic or rubber?
Plastic/rubber are insulators. They protect us from electric shocks and prevent short circuits by keeping the conducting core from touching other conductors.
5) What is the difference between AC and DC?
DC (from cells) flows in one direction. AC (from wall sockets) changes direction periodically and is used for larger appliances.
6) How do you make a simple conduction tester?
Connect a cell and a lamp with two wires, leaving the free ends apart. Touch the free ends to both ends of a test object; if the lamp glows, the object is a conductor.
7) Why does LED polarity matter?
An LED allows current in only one direction. It glows when its longer lead (+) is connected to the battery’s positive and the shorter lead (–) to the negative.
8) What do the long and short lines in a cell symbol represent?
In the symbol, the long line represents the positive terminal and the short line represents the negative terminal.
9) Why do devices sometimes place cells side-by-side?
To save space and shape the battery pack. Inside, metal strips still connect + of one cell to – of the next to make a series battery.
10) Why must we never experiment with mains electricity in school?
Mains AC can be dangerous and cause serious injury. School experiments should use only cells/batteries under teacher supervision.
📝Section 5 — Short Answers (10) • 3–4 lines each
1) Design an activity to identify which of six given cells are working.
Items: a small lamp/LED, two wires, and a known-good cell holder. Procedure: Test each cell one-by-one in the holder, completing a circuit with the lamp. If the lamp glows, the cell works; if not, label it faulty. Confirm with a second trial to avoid loose-connection errors.
2) Why are multiple cells often used in series?
Series connection increases the total voltage and energy available, helping lamps glow brighter and/or for longer. It also allows devices that need higher voltage to operate correctly.
3) Describe how to build and test a simple switch using a safety pin.
Fix two drawing pins on a cardboard; mount a safety pin so its free end can touch the second pin. Connect wires to the pins. When the safety pin touches both pins (closed), the circuit completes and the lamp glows; when separated (open), it does not.
4) Explain how to classify materials as conductors or insulators using a tester.
Use a tester (cell + lamp + wires). Touch the free ends to both ends of an object. If the lamp lights, the object conducts (metal key, foil). If not, it’s an insulator (plastic, rubber, wood). Record results in a table for multiple objects.
5) Write the steps to connect a cell and a lamp when holders are not available.
Strip ~1 cm insulation from wire ends. Tape one wire firmly to the cell cap (+) and the other to the flat base (–). Tape the other ends to the lamp terminals (tip and case), ensuring they don’t touch each other. Check connections are tight and the lamp should glow.
6) What does the LED symbol indicate about current and light?
The triangle points in the permitted current direction (towards the bar). Small outward arrows show that light is emitted. This reminds us the LED must be connected with correct polarity to glow.
7) How are side-by-side cells inside a device actually connected?
A metal strip connects the positive terminal of one cell to the negative of the next, creating a series battery. Polarity marks (+/–) in the compartment guide correct placement.
8) List four safety rules for working with circuits in school.
Use only cells/batteries (no mains). Keep hands dry; don’t touch bare conductors. Inspect wires for damaged insulation. Disconnect the battery when not testing to avoid heating and accidents.
9) Differentiate between an open and a closed circuit with an example.
Open circuit: there’s a gap (e.g., switch OFF); current cannot flow; the lamp stays off. Closed circuit: no gap (switch ON); current flows from cell + to – through the lamp, which then glows.
10) Explain why a lamp may not glow even if the switch is ON.
Possible faults: reversed LED polarity, fused filament bulb, loose/oxidised connections, unstripped wire insulation, dead cell(s), or broken wire. Check each link in the circuit systematically to find and fix the issue.