Exercise Solutions Available
Step-by-step answers for all textbook questions in this chapter
NCERT Solutions for Class 6 Science Chapter 12 — Electricity and Circuits
Key Concepts at a Glance
| Term | Definition |
|---|---|
| Electric cell | A device that produces electricity from chemicals stored inside it; has a positive terminal (metal cap) and a negative terminal (metal disc) |
| Electric bulb | A device that produces light when electric current passes through it; contains a thin wire called a filament |
| Filament | A thin coiled wire inside a bulb that glows when current passes through it; usually made of tungsten |
| Electric circuit | A complete path through which electric current can flow from one terminal of a cell, through the device, and back to the other terminal |
| Closed circuit | A circuit with no breaks; current flows and the bulb glows |
| Open circuit | A circuit with a break; current does not flow and the bulb does not glow |
| Switch | A device used to open or close a circuit; allows us to turn a device on or off |
| Conductor | A material that allows electric current to pass through it easily — e.g., copper, aluminium, iron, gold, silver |
| Insulator | A material that does not allow electric current to pass through it — e.g., rubber, plastic, wood, glass, ceramic |
| Battery | A combination of two or more electric cells connected together; provides more voltage than a single cell |
| Terminal | A point where a wire can be connected; each cell has a positive (+) terminal and a negative (−) terminal |
| Electric current | The flow of electric charge through a conductor; flows from the positive terminal of the cell, through the circuit, and back to the negative terminal |
Intext Questions (with Answers)
Intext Question 1 (Page 122)
What is an electric cell? Describe its parts.
An electric cell is a device that produces electricity from the chemicals stored inside it. It is the most common source of electric current in small devices like torches, clocks, and toys.
Parts of an electric cell:
1. Positive terminal — A small metal cap on top of the cell, usually marked with a plus (+) sign. 2. Negative terminal — A flat metal disc at the bottom of the cell, usually marked with a minus (−) sign. 3. Chemicals — Stored inside the cell, these chemicals react to produce electrical energy. 4. Metal body — The outer casing of the cell that holds everything together.
The cell produces electricity when the chemicals inside react. When the positive and negative terminals are connected through a circuit, electric current flows.
Intext Question 2 (Page 123)
How does a bulb glow? What happens when the filament breaks?
How a bulb glows: 1. When electric current passes through the thin filament wire inside the bulb, the filament becomes hot and starts glowing. 2. The filament is made of tungsten, which has a very high melting point and can glow white-hot without melting. 3. The bulb is filled with inert gases (like argon and nitrogen) to prevent the filament from oxidising (burning up).
When the filament breaks: 1. The circuit becomes open (incomplete). 2. Current can no longer flow through the bulb. 3. The bulb does not glow. 4. Such a bulb is called a fused bulb and needs to be replaced.
Intext Question 3 (Page 124)
What is an electric circuit? Draw a simple electric circuit with a cell, a bulb, and wires.
An electric circuit is a complete path through which electric current flows. It consists of:
1. A source of electricity — an electric cell or battery 2. Connecting wires — to carry current from one component to another 3. A device — a bulb (or any other electrical device) that uses the electricity
In a simple circuit:
- One wire connects the positive terminal of the cell to one terminal of the bulb.
- Another wire connects the other terminal of the bulb to the negative terminal of the cell.
- This creates a closed circuit, and the bulb glows.
Key rule: The circuit must be complete (closed) for the bulb to glow. If there is any break in the circuit, it becomes an open circuit and the bulb does not glow.
Intext Question 4 (Page 125)
What is the difference between an open circuit and a closed circuit?
| Feature | Closed Circuit | Open Circuit |
|---|---|---|
| Definition | A circuit with no breaks — current flows continuously | A circuit with a break — current does not flow |
| Path | Complete path from positive to negative terminal | Incomplete path — break somewhere in the circuit |
| Bulb | Bulb glows | Bulb does not glow |
| Switch | Switch is in the ON position | Switch is in the OFF position |
| Example | Connected wire from cell to bulb with no gaps | Disconnected wire, broken filament, or switch in OFF position |
Intext Question 5 (Page 126)
What is a switch? What is its function in an electric circuit?
A switch is a device that is used to make or break an electric circuit. It allows us to control the flow of electric current.
Function of a switch:
1. To open the circuit (switch OFF): When the switch is in the OFF position, it creates a break in the circuit. Current stops flowing and the device (bulb) turns off. 2. To close the circuit (switch ON): When the switch is in the ON position, it completes the circuit. Current flows and the device (bulb) turns on.
Types of switches:
- Toggle switch — Used in homes (light switches)
- Push button switch — Used in doorbells
- Slide switch — Used in torches and toys
Without a switch, we would have to connect and disconnect wires every time we want to turn a device on or off.
Intext Question 6 (Page 127)
Why do electricians use rubber gloves and rubber-soled shoes while working with electricity?
Electricians wear rubber gloves and rubber-soled shoes because:
1. Rubber is an insulator — it does not allow electric current to pass through it. 2. Protection from electric shock — If the electrician accidentally touches a live wire, the rubber gloves and shoes prevent the current from passing through their body. 3. Breaks the circuit through the body — Without rubber, current could flow through the electrician's body to the ground, causing a severe electric shock or even death. 4. Safety standard — This is a mandatory safety practice for anyone working with electrical wiring and equipment.
Rubber acts as a barrier between the electrician and the electric current, keeping them safe.
Intext Question 7 (Page 128)
Classify the following as conductors or insulators: Copper, rubber, aluminium, glass, iron, plastic, gold, wood, silver, ceramic.
| Conductors | Insulators |
|---|---|
| Copper | Rubber |
| Aluminium | Glass |
| Iron | Plastic |
| Gold | Wood |
| Silver | Ceramic |
- Conductors are materials that allow electric current to pass through them. Most metals are good conductors because they have free electrons that carry current.
- Insulators are materials that do not allow electric current to pass through them. They are used to cover wires and prevent electric shock.
Intext Question 8 (Page 129)
Why are electric wires covered with plastic or rubber?
Electric wires are covered with plastic or rubber because:
1. Plastic and rubber are insulators — They do not allow electric current to pass through them. 2. Safety — The insulating covering prevents us from getting an electric shock if we accidentally touch the wire. 3. Prevent short circuits — Without the covering, two bare wires touching each other would create a short circuit, causing sparks, fire, or damage to the circuit. 4. Current flows only through the metal wire — The covering ensures that current flows only through the intended path (the metal conductor inside) and does not leak out.
The metal inside the wire (usually copper) is the conductor that carries the current. The plastic/rubber covering is the insulator that keeps the current safely inside.
Intext Question 9 (Page 129)
Would the bulb glow in the following cases? Give reasons.
(a) One end of the wire is connected to the positive terminal of the cell and the other end is left free.
(b) Both ends of the wire are connected to the positive terminal of the cell.
(c) One end of the wire is connected to the positive terminal and the other end is connected to the negative terminal, with the bulb in the circuit.
Intext Question 10 (Page 130)
What would happen if the current flows from the negative terminal to the positive terminal of the cell?
In reality, electric current is the flow of electrons, and electrons flow from the negative terminal to the positive terminal inside the circuit. However, by convention, we say that conventional current flows from the positive terminal to the negative terminal outside the cell.
Whether we think of current flowing from positive to negative (conventional) or negative to positive (electron flow), the important thing is:
1. The circuit must be complete for current to flow at all. 2. The direction of flow does not affect the brightness of the bulb — the bulb glows equally in either direction. 3. The bulb glows as long as there is a complete circuit regardless of which terminal we connect first.
What matters for the bulb to glow is a complete (closed) circuit, not the direction of current flow.
Exercise Questions (with Answers)
Exercise Question 1
Fill in the blanks:
(a) A device that can break an electric circuit is called a \_\_\_\_\_\_.
A switch is used to open (break) or close (complete) an electric circuit.
(b) An electric cell has \_\_\_\_\_\_ terminals.
An electric cell has two terminals — a positive terminal (metal cap) and a negative terminal (metal disc).
Exercise Question 2
Mark 'True' or 'False' for the following statements:
(a) Electric current can flow through metals.
(b) Instead of metal wires, a jute string can be used to make a circuit.
(c) Electric current can pass through a sheet of thermocol.
Exercise Question 3
Explain why the bulb does not glow when a safety pin is replaced by a rubber band in a simple electric circuit.
A safety pin is made of metal (usually steel or brass), which is a conductor of electricity. When the safety pin is in the circuit, current flows through it and the bulb glows.
A rubber band is an insulator — it does not allow electric current to pass through it. When the safety pin is replaced by a rubber band:
1. Current cannot flow through the rubber band. 2. The circuit becomes incomplete (open circuit). 3. There is no complete path for the current. 4. The bulb does not glow.
This shows that conductors (like metal) allow current to flow, while insulators (like rubber) block the flow of current.
Exercise Question 4
What is the purpose of using a switch in an electric circuit?
A switch is used to control the flow of electric current in a circuit. Its purposes include:
1. Turning a device on or off — When the switch is ON (closed), current flows and the device works. When the switch is OFF (open), current stops and the device turns off. 2. Safety — A switch allows us to disconnect the circuit when not in use, preventing wastage of electricity and reducing risk. 3. Convenience — Instead of connecting and disconnecting wires, we simply flip the switch. 4. Emergency — In case of danger, the switch can quickly cut off the power.
Without a switch, we would have to connect or disconnect wires every time we want to use or stop an electrical device.
Exercise Question 5
Using the "conductor tester" on an object, it was found that the bulb begins to glow. Is the object a conductor or an insulator? Explain.
The object is a conductor.
- In a conductor tester, the object is placed between two gaps in the circuit.
- If the bulb glows, it means current is flowing through the object and completing the circuit.
- Only conductors allow electric current to pass through them.
- If the object were an insulator, current would not flow and the bulb would not glow.
Therefore, since the bulb glows, the object must be a conductor of electricity.
Exercise Question 6
Why do we cover electric wires with plastic covering?
We cover electric wires with plastic because:
1. Plastic is an insulator — It does not allow electric current to pass through. 2. Prevents electric shock — If we touch a bare (uncovered) wire carrying current, we would get a shock. The plastic covering prevents this. 3. Prevents short circuits — If two bare wires touch each other, current can jump between them, causing a short circuit. The plastic covering keeps the wires separated. 4. Protects the metal wire inside — The plastic covering protects the copper wire inside from damage, corrosion, and wear.
The metal conductor (usually copper) inside the wire carries the current, and the plastic insulation outside keeps the current safely contained.
Exercise Question 7
Will the bulb glow in the following circuit? Give reasons.
A circuit where one wire goes from the positive terminal of the cell to the bulb, and another wire goes from the negative terminal of the cell to the same terminal of the bulb (both wires are connected to the same terminal of the bulb).
No, the bulb will not glow.
Reason: Both wires are connected to the same terminal of the bulb. This means current flows from the cell to one terminal of the bulb, but it cannot flow through the filament because there is no return path from the other terminal of the bulb back to the cell.
For the bulb to glow:
- One wire must connect to one terminal of the bulb.
- The other wire must connect to the other terminal of the bulb.
- Only then does current flow through the filament, making it glow.
In this case, since both wires are on the same terminal, current does not pass through the filament, and the bulb does not glow.
Exercise Question 8
Name some materials that are conductors of electricity. Also name some insulators.
Conductors of electricity:
| Material | Why it conducts |
|---|---|
| Copper | Metal with free electrons; widely used in wires |
| Aluminium | Metal; used in overhead power lines |
| Iron | Metal; used in many electrical applications |
| Gold | Excellent conductor; used in high-quality electronics |
| Silver | Best conductor of electricity |
| Brass | Alloy of copper and zinc; used in switches and plugs |
| Tap water | Contains dissolved salts that conduct electricity |
Insulators of electricity:
| Material | Why it insulates |
|---|---|
| Rubber | No free electrons; used for gloves and wire covering |
| Plastic | No free electrons; used for wire insulation and switch casings |
| Wood | Does not conduct; used for electric poles (dry wood) |
| Glass | No free electrons; used in electrical insulators |
| Ceramic | Used in high-voltage insulators on electric poles |
| Air | Generally an insulator; prevents current leakage |
| Dry cloth | Does not conduct; used as insulation |
Exercise Question 9 (MCQ)
Which of the following is a conductor of electricity?
(a) Rubber ✗ (b) Plastic ✗ (c) Copper ✓ (d) Wood ✗
Copper is a metal and a good conductor of electricity. It has free electrons that carry electric current. Rubber, plastic, and wood are insulators — they do not allow current to pass through.
Exercise Question 10 (MCQ)
Which of the following is used to open or close an electric circuit?
(a) Bulb ✗ (b) Cell ✗ (c) Switch ✓ (d) Wire ✗
A switch is a device specifically designed to open (break) or close (complete) an electric circuit. It allows us to turn electrical devices on or off.
Multiple Choice Questions (MCQs)
MCQ 1
An electric cell has:
(a) One terminal ✗ (b) Two terminals ✓ (c) Three terminals ✗ (d) No terminals ✗
An electric cell has two terminals — a positive terminal (metal cap on top) and a negative terminal (flat metal disc at the bottom).
MCQ 2
A bulb has:
(a) One terminal ✗ (b) Two terminals ✓ (c) Three terminals ✗ (d) No terminals ✗
A bulb has two terminals — the side of the metal casing and the bottom tip. Current enters through one terminal, flows through the filament, and exits through the other terminal.
MCQ 3
Which of the following will make the bulb glow in a circuit?
(a) Connecting both wires to the same terminal of the bulb ✗ (b) Leaving one wire disconnected ✗ (c) Using a jute string instead of a wire ✗ (d) Completing the circuit with copper wire and a switch ✓
Only a complete (closed) circuit allows current to flow. Copper wire is a conductor, and a switch in the ON position closes the circuit. Options (a), (b), and (c) all create open circuits.
MCQ 4
Tap water conducts electricity because:
(a) It is a pure substance ✗ (b) It contains dissolved salts and minerals ✓ (c) Water itself is a good conductor ✗ (d) It has no free electrons ✗
Pure water is a poor conductor of electricity. Tap water contains dissolved salts and minerals that make it conductive. This is why we should not touch electrical appliances with wet hands.
MCQ 5
A fused bulb does not glow because:
(a) The cell is weak ✗ (b) The filament is broken ✓ (c) The switch is off ✗ (d) The wires are thick ✗
A fused bulb has a broken filament. The filament is the thin wire inside the bulb that glows when current passes through it. When it breaks, the circuit inside the bulb is open, and current cannot flow.
MCQ 6
Which of the following is NOT a good conductor of electricity?
(a) Silver ✗ (b) Copper ✗ (c) Gold ✗ (d) Rubber ✓
Silver, copper, and gold are all metals and excellent conductors. Rubber is an insulator and does not allow electric current to pass through it.
Common Mistakes
1. Confusing a cell with a battery: A cell is a single unit that produces electricity. A battery is a combination of two or more cells connected together. A single AA cell is a cell; a 9V battery contains multiple cells inside.
2. Thinking pure water is a good conductor: Pure (distilled) water is actually a poor conductor. Tap water conducts electricity because of dissolved salts and minerals. This is why we should never touch electrical switches with wet hands — the salts in our sweat make water conductive.
3. Connecting both wires to the same terminal: For a bulb to glow, one wire must connect to each terminal of the bulb. Connecting both wires to the same terminal does not allow current to flow through the filament.
4. Believing insulators can never conduct: Under extreme conditions (very high voltage), even insulators can break down and conduct electricity. For Class 6, we treat insulators as non-conductors, but in reality, no insulator is perfect.
5. Forgetting that the filament is part of the circuit: The filament inside the bulb is the part that glows. It is part of the circuit path. If the filament breaks, the circuit is broken, and the bulb does not glow — even if everything else is connected correctly.
Exam Checklist
- [ ] Can you identify the parts of an electric cell (positive and negative terminals)?
- [ ] Can you draw a simple electric circuit with a cell, wires, and a bulb?
- [ ] Can you explain the difference between an open circuit and a closed circuit?
- [ ] Can you classify common materials as conductors or insulators?
- [ ] Can you explain why bulb wires are covered with plastic/rubber insulation?
- [ ] Can you explain what a switch does and why it is needed?
- [ ] Can you explain why a fused bulb does not glow?
- [ ] Can you determine whether a bulb will glow given a circuit diagram?