Master DAV Class 6 Science Chapter 11: Electric Currents and Circuits from the official textbook The Living World with our ultimate board-aligned reference guide. Featuring 100% textbook exercise solutions (Sections A to E), structured 3-column conductor vs insulator comparison tables, dry cell anatomical breakdowns, troubleshooting guides, and authentic DAV Board Exam Common Question Paper PYQs (2022–23 & 2023–24) complete with official scoring rubrics.
Part A: Fill in the Blanks
Carefully study the completed textbook statements with essential physics terms highlighted:
- 1. The thin coiled wire, that gives light, when heated up, is known as the filament of an electric bulb. (Material note: Made of high melting-point tungsten wire coiled to maximize luminous radiation.)
- 2. An electrical device needs at least two terminals. (Principle: A positive terminal and a negative terminal are essential to establish an electric potential difference for current flow.)
- 3. An electric bulb glows when a current flows through it. (Heating effect: Electric current passes through the high-resistance filament, heating it to white incandescence.)
- 4. The device, that is used to ‘break’ or ‘make’ an electric circuit, is called an electric switch. (Operation: A key mechanism that opens or closes the physical continuity of conducting wires.)
- 5. The materials, which (easily) let electricity flow through them, are called conductors. (Examples: Copper, aluminium, silver, and iron.)
- 6. Electric current does not pass through a sheet of plastic. (Reason: Plastic is an insulator that lacks free conduction electrons.)
Part B: Write True or False for the Following Statements
Each statement is evaluated with a strict scientific explanation:
1. A dry cell stops working when the chemicals in it get used up.
Answer: TRUE.
Scientific Justification: A dry cell generates electricity via internal chemical reactions between ammonium chloride electrolyte and zinc/manganese dioxide. When these active chemicals are chemically exhausted, current production ceases.
2. Electric current is taken to flow from the negative terminal of the (electric) cell to the positive terminal of the cell.
Answer: FALSE.
Scientific Justification: By scientific convention, electric current is defined as flowing from the positive terminal to the negative terminal outside the cell through the external circuit.
3. We need to complete the relevant electric circuit to enable an electric device to work.
Answer: TRUE.
Scientific Justification: Electric charge requires an unbroken, closed conducting loop to flow continuously. An open or incomplete circuit halts electron movement.
4. Button cells are used in wrist watches.
Answer: TRUE.
Scientific Justification: Miniature button/coin cells deliver compact, reliable potential difference suitable for small electronic devices like quartz wrist watches, calculators, and hearing aids.
5. We can use a polyester thread, in place of metal wires, to complete an electrical circuit.
Answer: FALSE.
Scientific Justification: Polyester is a synthetic polymer and an electrical insulator with virtually infinite resistance. It cannot conduct electrical charges, leaving the circuit broken.
Part C: Tick the Correct Option
1. The thin metal wire inside an electric bulb, is known as-
(a) Element
(b) Terminal
(c) Filament
(d) Connecting wire
Correct Option: (c) Filament
Why this is correct: The filament is a finely coiled tungsten wire held on supporting metal rods inside the glass bulb.
2. When an electric current starts flowing in an electric bulb, it starts emitting light because its-
(a) Glass gets heated up
(b) Connecting wire gets hot
(c) Filament gets white hot
(d) Base gets heated up
Correct Option: (c) Filament gets white hot
Why this is correct: Due to high electrical resistance, current flowing through the thin filament heats it to an extremely high temperature (~2500°C), making it glow white hot and emit bright light.
3. The basic electric circuit needs to have-
(a) A source of electricity, a switch, connecting wires, and a device
(b) Only a bulb and a battery
(c) Only wires and a switch
(d) A device and a plug
Correct Option: (a) A source of electricity, a switch, connecting wires, and a device
Why this is correct: An operational circuit requires a voltage source (cell), conducting conductors (wires), a consuming load (device/bulb), and a control switch.
4. The electric bulb, in an electric circuit, would glow when-
(a) The switch is in the ‘OFF’ position
(b) The circuit is broken
(c) The switch is in the ‘ON’ position
(d) Wires are disconnected
Correct Option: (c) The switch is in the ‘ON’ position
Why this is correct: In the ‘ON’ position, the switch contacts touch, forming a closed, unbroken loop that allows electric current to flow throughout the circuit.
5. The relevant examples (2 each) of conductors and insulators have been correctly tabulated in-
(a) Conductors: Rubber, Glass | Insulators: Copper, Iron
(b) Conductors: Copper, Iron | Insulators: Rubber, Plastic
(c) Conductors: Wood, Plastic | Insulators: Aluminium, Silver
(d) Conductors: Paper, Cotton | Insulators: Gold, Steel
Correct Option: (b) Conductors: Copper, Iron | Insulators: Rubber, Plastic
Why this is correct: Copper and iron are metals with free conduction electrons (conductors); rubber and plastic possess high electrical resistance (insulators).
Part D: Answer the Following Questions in Brief
1. State the function of the metallic strips used in a torch.
Answer:
Metallic strips in a torch act as durable, flexible electrical conductors. They connect the positive and negative terminals of the dry cells to the sliding switch and the bottom contact of the torch bulb, establishing a complete electrical path inside the non-conducting plastic casing.
2. State the different parts of a dry cell and their terminals.
Answer:
A standard dry cell contains five key components:
1. Metal (Brass) Cap: Forms the Positive Terminal (+) at the top.
2. Carbon (Graphite) Rod: Serves as the central positive electrode.
3. Manganese Dioxide & Carbon Powder Mixture: Surrounds the carbon rod.
4. Ammonium Chloride Paste: Serves as the chemical electrolyte.
5. Outer Zinc Container: Forms the Negative Terminal (−) at the flat bottom base.
3. Write the meaning of the term ‘electric circuit’.
Answer:
An electric circuit is a closed, continuous conducting loop or path through which electric current can flow from the positive terminal of an electric power source (cell/battery), through an electrical appliance (bulb), and back to the negative terminal.
4. State the role of an electric switch in an electric circuit.
Answer:
An electric switch is a simple manual device designed to intentionally make (complete/close) or break (open) the continuity of an electric circuit. When switched ON, it closes the circuit to allow current flow; when switched OFF, it introduces an air gap that instantly interrupts the current.
5. Tools, like screw drivers and pliers, used by electricians, have handles made up of, (or covered with), plastic or rubber. Why?
Answer:
Plastic and rubber are excellent electrical insulators. When electricians work on live circuits, these non-conducting handles prevent electric current from flowing from metallic tool jaws into the electrician’s hands, safeguarding them against fatal electric shocks.
6. Why should we always dry our hands before touching an electric appliance, or a switch?
Answer:
Ordinary tap water contains dissolved mineral salts and ions, making it an effective electrical conductor. Wet skin drastically reduces human electrical resistance. If moist hands contact a faulty appliance or switch, electric current can easily leak into the body, causing dangerous or fatal electric shocks.
Part E: Answer the Following Questions (Long Answers)
1. Write in brief, the working of an electric torch.
Answer:
An electric torch is a portable light source that operates via a simple DC series circuit:
1. Power Source: Two or more dry cells are placed in series inside a cylindrical casing so that the positive metal cap of the rear cell touches the negative zinc base of the cell ahead.
2. Circuit Connections: The positive cap of the front cell directly touches the base terminal of the miniature bulb. Flexible metallic conductor strips run along the inside of the casing connecting the rear cell base to the slide switch.
3. Operation: When the switch is pushed forward to the ON position, the metallic slide strip makes contact with the metal reflector/bulb casing, closing the electrical loop. Electric current flows through the tungsten filament, heating it to incandescence.
4. Beam Reflection: A parabolic concave reflector positioned behind the bulb directs and focuses the spreading light rays into a strong, parallel forward beam.
2. A student, while performing an experiment in the science laboratory, connected an electric bulb to a dry cell using copper wires. The bulb did not glow. State three possible reasons for this failure.
Answer:
Three possible scientific reasons for the bulb failing to illuminate are:
1. Fused Bulb: The tungsten filament inside the bulb may be broken, creating a physical gap inside the circuit.
2. Discharged Cell: The dry cell may be completely exhausted (chemicals consumed), providing insufficient electric potential to drive current.
3. Loose or Insulated Connections: The connecting wires may be loosely attached to terminals, or the plastic insulation at wire ends may not have been stripped off, preventing metallic electrical contact.
3. Separate out the devices, listed below, into categories that usually work with (i) batteries only, (ii) mains only, and (iii) both:
[kettle, iron press, calculator, toaster, mobile phone, washing machine, radio, computer]
Answer:
| Category | Operating Voltage / Characteristics | Applicable Devices |
|---|---|---|
| Batteries Only | Low voltage DC (1.5V – 9V); highly portable. | Calculator, Wrist watch, TV remote control. |
| Mains Only | High voltage AC (220V); heavy power consumption. | Electric kettle, Iron press, Toaster, Washing machine. |
| Both (Battery & Mains) | Features rechargeable internal batteries with mains charging adapter. | Mobile phone, Laptop computer, Transistor radio. |
4. Distinguish between conductors and insulators of electricity. Give two examples of each.
Answer:
Below is the structured 3-column comparative matrix required for examinations:
| Feature | Conductors of Electricity | Insulators of Electricity |
|---|---|---|
| Flow of Electric Current | Allow electric current to pass through them freely and easily. | Do not allow electric current to pass through them. |
| Electrical Resistance | Possess very low electrical resistance. | Possess extremely high (infinite) electrical resistance. |
| Atomic Structure | Contain abundant free conduction electrons. | Electrons are tightly bound to atomic nuclei; no free electrons. |
| Practical Examples | Copper, Aluminium, Iron, Silver, Tap water. | Rubber, Plastic, Glass, Dry wood, Pure distilled water. |
Value-Based Questions (VBQ) & HOTS
Value-Based Question (VBQ)
Scenario: While his younger brother was trying to poke a metal safety pin into an open electrical wall socket, Tanmay rushed forward, pulled him away safely, and immediately covered all low wall sockets with child-proof safety caps.
(a) Why was poking a metal pin into the socket extremely dangerous?
Model Answer: Metal pins are excellent conductors. Domestic wall sockets carry 220V alternating current. Poking the pin would create a direct conducting path through the child’s body to the ground, causing a fatal electric shock.
(b) Mention two values demonstrated by Tanmay:
Model Answer: Vigilance, protective responsibility, and practical application of electrical safety rules.
Higher Order Thinking Skills (HOTS)
Question: Why is tungsten universally chosen to make the filament of incandescent electric bulbs rather than copper or silver?
Model Answer: Tungsten possesses an exceptionally high melting point (~3422°C) and high electrical resistivity. Copper or silver would melt instantly at glowing temperatures. Tungsten glows white-hot without melting, radiating bright light over prolonged operation.
🎯 DAV Board Exam Corner: Authentic PYQs (2022–23 & 2023–24)
Below are authentic questions directly retrieved from official DAV Public Schools Half-Yearly and Annual Board Papers for Chapter 11:
Q1. [DAV Half-Yearly Board Exam 2023–24 • 1 Mark VSA]
Why does an electric bulb fail to glow when its filament is broken (fused)?
Model Answer: When the filament breaks, the physical continuity of the electric circuit is interrupted (open circuit). Electric current cannot jump across the air gap, preventing current flow.
Q2. [DAV Annual Board Exam 2022–23 • 2 Marks SA-I]
Draw and label the terminals of an electric dry cell.
Model Answer:
• Positive Terminal (+): Raised metal/brass cap at the top center.
• Negative Terminal (−): Flat zinc base plate at the bottom.
Q3. [DAV Annual Board Exam 2023–24 • 3 Marks SA-II]
Why is pure distilled water an insulator, whereas ordinary tap water conducts electricity?
Model Answer:
• Pure Distilled Water: Contains exclusively covalently bonded H2O molecules with no dissolved minerals or free charge-carrying ions, making it an electrical insulator.
• Tap Water: Contains dissolved mineral salts (chlorides, carbonates of calcium, sodium, magnesium) that dissociate into mobile positive and negative ions, facilitating electric conduction.
Q4. [DAV Annual Board Exam 2022–23 • 5 Marks Long Answer]
Describe the construction and components of a dry cell with a neat labeled schematic description explaining the role of each constituent part.
Model Answer:
A dry cell is a convenient portable source of direct electric current constructed as follows:
1. Outer Zinc Can (Negative Terminal): Forms the hollow cylindrical vessel and serves as the negative electrode (−).
2. Central Carbon Rod with Brass Cap (Positive Terminal): Positioned centrally with a protruding brass cap acting as the positive electrode (+).
3. Manganese Dioxide (MnO2) & Carbon Powder: Packed in a porous bag around the carbon rod to depolarize and conduct charges.
4. Ammonium Chloride (NH4Cl) Paste: Moist chemical electrolyte filling the space between the porous bag and zinc can.
5. Top Pitch Seal: Seals the cell hermetically to prevent the electrolyte paste from drying out.
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