How to Use This Page
Read each question carefully and try to answer it on your own before checking the solution. Use the Key Concepts table for a quick refresher, and pay special attention to the Common Mistakes section to avoid losing marks in exams. The Exam Checklist at the end helps you track whether you have covered every important topic.
Key Concepts (Quick Recap)
| Term | Definition |
|---|---|
| Magnet | An object that attracts magnetic materials (iron, nickel, cobalt) and has two poles — north and south. |
| Magnetic Poles | The two regions of a magnet where the magnetic force is strongest: the north-seeking pole and the south-seeking pole. |
| Magnetic Field | The region around a magnet where its magnetic influence can be detected and measured. |
| Magnetic Field Lines | Imaginary lines that represent the direction and strength of a magnetic field, emerging from the north pole and entering the south pole outside the magnet. |
| Electromagnet | A temporary magnet created by passing electric current through a coil of wire wound around a soft iron core; its magnetism can be switched on or off. |
| Permanent Magnet | A magnet that retains its magnetism for a long time, typically made from steel or alloys like Alnico. |
| Lodestone | A naturally occurring magnetic mineral (magnetite, Fe₃O₄) that was one of the earliest known magnets. |
| Magnetic Induction | The process by which a piece of iron becomes magnetised when placed near a magnet, without direct physical contact. |
| Curie Temperature | The temperature above which a ferromagnetic material loses its permanent magnetism and becomes paramagnetic. |
| Compass | A navigation device with a magnetic needle that freely rotates and aligns in the north-south direction, used to find direction. |
| Retentivity | The ability of a magnetic material to retain magnetism after the magnetising force is removed; high in steel, low in soft iron. |
| Permeability | The measure of how easily a material can be magnetised; soft iron has high permeability, making it ideal for electromagnet cores. |
I. Choose the Best Answer (MCQs)
Q1. Which of the following is a natural magnet?
- (a) Bar magnet (b) Horseshoe magnet (c) Lodestone (d) Electromagnet
Q2. Like poles of two magnets
- (a) Attract each other (b) Repel each other (c) Cancel each other (d) Have no effect
Q3. A magnet always points in the ______ direction when freely suspended.
- (a) East-West (b) North-South (c) North-East (d) South-West
Q4. Which of the following is NOT a magnetic material?
- (a) Iron (b) Nickel (c) Cobalt (d) Wood
Q5. The magnetic field is strongest at the
- (a) Centre of the magnet (b) Poles of the magnet (c) Midpoint between the poles (d) Along the sides
Q6. Magnetic field lines
- (a) Cross each other (b) Start from south pole and end at north pole (c) Start from north pole and end at south pole (d) Do not form closed loops
Q7. An electromagnet is a magnet that works on
- (a) Chemical energy (b) Magnetic energy (c) Electric energy (d) Sound energy
Q8. The device used to find direction is called a
- (a) Barometer (b) Thermometer (c) Magnetic compass (d) Manometer
Q9. The temperature at which a magnet loses its magnetism completely is called
- (a) Boiling point (b) Curie temperature (c) Melting point (d) Freezing point
Q10. Magnetic induction refers to
- (a) A magnet losing its poles when heated (b) An iron piece becoming a magnet when placed near another magnet (c) Electric current producing a magnetic field (d) Two magnets attracting each other
Q11. A magnetic compass needle aligns in the north-south direction because
- (a) The needle is attracted by the Sun (b) The Earth behaves like a giant magnet (c) Wind pushes the needle (d) The needle is made of steel
II. Fill in the Blanks
1. The north pole of a magnet repels the north pole of another magnet. 2. The region around a magnet where its influence can be detected is called the magnetic field. 3. Magnetic field lines are closer near the poles of a magnet. 4. A freely suspended magnet always rests in the north-south direction. 5. The natural magnet is called lodestone. 6. The process of converting an iron rod into a magnet by using another magnet is called magnetic induction. 7. An electromagnet is a temporary magnet. 8. Materials that are not attracted by magnets are called non-magnetic materials. 9. The path along which a free north pole tends to move is called a magnetic field line. 10. Unlike poles attract each other. 11. The temperature at which a magnet loses its magnetism is called the Curie temperature. 12. A compass is a device that uses a magnetic needle to find direction.
III. True or False
IV. Match the Following
| Column I | Column II | Answer |
|---|---|---|
| Natural magnet | Lodestone | Natural magnet — Lodestone |
| Artificial magnet | Bar magnet | Artificial magnet — Bar magnet |
| Temporary magnet | Electromagnet | Temporary magnet — Electromagnet |
| Permanent magnet | Steel magnet | Permanent magnet — Steel magnet |
| Magnetic material | Iron | Magnetic material — Iron |
V. Short Answer Questions
Q1. What are the properties of magnets? Answer: Magnets possess several distinctive properties that distinguish them from ordinary objects. A magnet attracts magnetic materials like iron, nickel, and cobalt, pulling them towards itself when they are nearby. Every magnet has two poles — a north pole and a south pole — and these poles cannot be separated from each other. Like poles repel each other (N-N or S-S), while unlike poles attract each other (N-S). When a magnet is freely suspended, it always aligns itself in the north-south direction because of the Earth's magnetic field. Additionally, magnetic poles always exist in pairs; even if a magnet is broken into pieces, each piece will have both a north pole and a south pole.
Q2. What is the difference between a natural magnet and an artificial magnet? Answer: Natural magnets and artificial magnets differ in several important ways. Natural magnets, such as lodestone, are found in nature and have irregular shapes with relatively weak magnetic strength. Artificial magnets, on the other hand, are manufactured by humans in definite shapes like bar magnets, horseshoe magnets, and magnetic needles, and they are much stronger than natural magnets. Because of their weakness and irregular shape, natural magnets have limited practical use, while artificial magnets are used widely in motors, generators, speakers, and many other devices.
| Property | Natural Magnet | Artificial Magnet |
|---|---|---|
| Occurrence | Found in nature (lodestone) | Made by humans |
| Strength | Weak | Strong |
| Shape | Irregular | Definite shape (bar, horseshoe, etc.) |
| Use | Limited | Wide range of applications |
Q3. What is magnetic induction? Answer: Magnetic induction is the process by which a piece of iron or steel becomes magnetised when it is placed near a magnet, even without direct physical contact. When the iron piece is brought close to a magnet, the magnet's magnetic field causes the randomly arranged magnetic domains inside the iron to align in a particular direction. This alignment turns the iron piece into a temporary magnet, with the end nearest the magnet acquiring the opposite polarity. However, once the magnet is removed, the iron piece generally loses most of its induced magnetism because the domains return to their random arrangement.
Q4. How is an electromagnet different from a permanent magnet? Answer: An electromagnet and a permanent magnet differ fundamentally in how their magnetism is produced and controlled. An electromagnet is a temporary magnet that works only when electric current flows through its coil; its magnetism can be switched on or off by controlling the current. A permanent magnet, in contrast, retains its magnetism permanently and cannot be switched off. Additionally, electromagnets can be made very strong by increasing the current, adding more coil turns, or using a soft iron core, whereas permanent magnets have a fixed strength determined by the material they are made from.
Q5. Why is soft iron used as the core of an electromagnet? Answer: Soft iron is used as the core of an electromagnet for three important reasons. First, it has high magnetic permeability, which means it gets magnetised very easily and strongly when current flows through the coil. Second, it has low retentivity, meaning it loses almost all of its magnetism as soon as the current is switched off. Third, these two properties together make the electromagnet behave as a true temporary magnet — it gains strong magnetism instantly when current flows and loses it quickly when the current stops. If steel were used instead, it would retain magnetism even after the current is switched off, which would defeat the purpose of an electromagnet.
Q6. List three uses of electromagnets. Answer: Electromagnets are used in a wide variety of practical applications because their magnetism can be controlled. In electric bells and buzzers, an electromagnet repeatedly attracts and releases a hammer that strikes a bell to produce sound. In scrap yards, powerful electromagnets mounted on cranes lift and move heavy iron and steel objects, and the objects can be released simply by switching off the current. In hospitals, MRI (Magnetic Resonance Imaging) machines use very strong electromagnets to produce detailed images of internal body structures. Other important uses include magnetic separators for removing iron impurities, electric motors, generators, and circuit breakers.
Q7. What are magnetic field lines? State their characteristics. Answer: Magnetic field lines are imaginary lines used to represent the direction and strength of the magnetic field around a magnet. They provide a visual way to understand the invisible magnetic influence in the space around a magnet. The key characteristics of magnetic field lines are as follows: (1) They emerge from the north pole and enter the south pole outside the magnet. (2) They never intersect each other, because at any given point the magnetic field can have only one direction. (3) They are closer together where the field is stronger (near the poles) and farther apart where it is weaker. (4) They form closed loops, travelling from north to south outside the magnet and from south to north inside the magnet. (5) The tangent to a field line at any point gives the direction of the magnetic field at that point.
VI. Detailed Answer Questions
Q1. Describe an activity to show that a magnet has two poles and that like poles repel while unlike poles attract. Answer: This fundamental activity demonstrates two key properties of magnets — that every magnet has two distinct poles, and that like poles repel while unlike poles attract.
Activity: 1. Take two bar magnets and clearly mark their north and south poles using a compass or by comparing with a known magnet. 2. Suspend one magnet freely using a string so it can rotate without obstruction. 3. Bring the north pole of the second magnet close to the north pole of the suspended magnet and observe the result. 4. Now bring the north pole close to the south pole of the suspended magnet and observe the result. 5. Repeat the process by bringing the south pole close to both the north pole and south pole of the suspended magnet.
Observations:
- When like poles are brought close (N-N or S-S), the suspended magnet rotates away, showing repulsion.
- When unlike poles are brought close (N-S or S-N), the suspended magnet moves towards the approaching pole, showing attraction.
- In every case, each magnet shows two distinct poles — one that seeks the geographic north and one that seeks the geographic south.
- This confirms that every magnet has two poles and that magnetic interaction follows the rule: like poles repel, unlike poles attract.
Conclusion: The activity clearly shows that a magnet cannot have a single pole and that the nature of interaction depends on which poles face each other.
Q2. Explain the construction and working of an electromagnet with a diagram description. Answer: An electromagnet is one of the most useful applications of magnetism because its magnetic strength can be controlled by adjusting the electric current.
Construction: An electromagnet consists of three main components: 1. A soft iron core — typically U-shaped or straight, chosen for its high permeability and low retentivity. 2. A coil of insulated copper wire — wound tightly around the soft iron core in multiple turns. The insulation prevents short-circuiting between adjacent turns. 3. A battery or DC power supply — connected to the ends of the coil to provide electric current.
Applications: Electric bells, cranes in scrap yards, MRI machines, circuit breakers, loudspeakers, and magnetic separators all use electromagnets because the magnetism can be turned on and off as needed.
Q3. Explain why the Earth is considered a giant magnet and describe the magnetic field of the Earth. Answer: The Earth behaves as if a giant bar magnet is placed at its centre, with its magnetic axis tilted about 11.5 degrees from the geographic axis. This is the reason a compass needle aligns in the north-south direction and has been used for navigation for centuries.
Key points about the Earth's magnetism: 1. The Earth's magnetic south pole is located near the geographic north pole (in the Arctic region), and the Earth's magnetic north pole is located near the geographic south pole (in Antarctica). This is why a compass needle's north pole points toward the geographic north — it is attracted by the Earth's magnetic south pole located there. 2. The Earth's magnetic field extends far into space, forming a region called the magnetosphere. The magnetosphere acts as a shield, protecting the Earth from harmful solar radiation and charged particles emitted by the Sun. 3. The magnetic field lines emerge from near the geographic south (Earth's magnetic north), curve through space over thousands of kilometres, and enter near the geographic north (Earth's magnetic south). 4. The angle between the geographic meridian and the magnetic meridian at a place is called the magnetic declination. This angle varies from place to place and must be accounted for in precise navigation. 5. The Earth's magnetic field is not constant — it changes slowly over time, and the magnetic poles drift by several kilometres each year. Scientists believe the field is generated by the movement of molten iron in the Earth's outer core, a theory known as the dynamo effect.
Practical significance: The Earth's magnetic field enables compass navigation, protects the atmosphere from being stripped away by solar wind, and creates the auroras (northern and southern lights) near the poles.
Q4. Explain the method of making a magnet by (a) single touch method and (b) double touch method. Answer: Magnets can be created from magnetic materials using these two rubbing methods. Both methods work by aligning the randomly oriented magnetic domains in the material.
(a) Single Touch Method: This is the simpler of the two methods and is suitable for making weak magnets.
1. Take a steel rod and place it on a flat, clean surface. 2. Take a strong bar magnet and place one of its poles at one end of the steel rod. 3. Stroke the magnet along the length of the rod from one end to the other in one direction only — do not rub back and forth. 4. After each stroke, lift the magnet completely off the rod and return to the starting end. This is important because rubbing back and forth would disturb the alignment of the domains. 5. Repeat this process about 30 to 40 times, always stroking in the same direction. 6. The steel rod becomes magnetised, with the end where the strokes end acquiring the opposite polarity of the stroking pole. For example, if the south pole was used for stroking from left to right, the right end becomes a north pole.
(b) Double Touch Method: This method produces a stronger magnet because both poles of two magnets are used simultaneously.
1. Place a steel rod on a flat surface. 2. Take two bar magnets with opposite poles facing each other — for instance, the north pole of one and the south pole of the other. 3. Place both magnets at the centre of the rod and simultaneously stroke towards opposite ends. 4. At the ends, lift both magnets, return them to the centre, and repeat the process about 30 to 40 times. 5. The rod becomes a stronger magnet than one made with the single touch method because the combined influence of both poles aligns the magnetic domains more effectively and uniformly.
Important note: In both methods, the strokes must always be in the same direction. Stroking in alternate directions would misalign the domains and weaken or destroy the magnetisation.
Common Mistakes
- Saying magnets can have a single pole: Magnetic poles always exist in pairs; cutting a magnet creates two smaller magnets, each with both poles.
- Confusing magnetic and non-magnetic materials: Not all metals are magnetic. Only iron, nickel, and cobalt are ferromagnetic. Aluminium, copper, gold, and silver are non-magnetic metals.
- Confusing Earth's geographic and magnetic poles: The Earth's magnetic south pole is near the geographic north, and the magnetic north pole is near the geographic south.
- Confusing permanent and temporary magnets: Steel makes permanent magnets (retains magnetism); soft iron makes temporary magnets/electromagnets (loses magnetism quickly).
- Saying magnetic field lines can cross: Magnetic field lines never intersect. At any point, the magnetic field has only one direction.
- Confusing magnetic induction with electromagnetic induction: Magnetic induction makes iron magnetic by proximity to a magnet. Electromagnetic induction produces current when a conductor moves in a magnetic field.
- Confusing Curie temperature with melting point: The Curie temperature is the point at which a material loses its magnetic properties, not the point at which it melts. A magnet can lose its magnetism well below its melting point — for iron, the Curie temperature is about 770 degrees Celsius, while its melting point is about 1538 degrees Celsius.
- Thinking a compass points to geographic north because of geographic north's polarity: A compass needle's north pole is actually attracted to the Earth's magnetic south pole, which happens to be located near the geographic north. It is the magnetic attraction, not the geographic direction, that aligns the needle.
Exam Checklist
- [ ] Can you list the properties of magnets?
- [ ] Can you distinguish between natural and artificial magnets?
- [ ] Can you explain magnetic induction with an example?
- [ ] Can you describe the construction and working of an electromagnet?
- [ ] Can you list the characteristics of magnetic field lines?
- [ ] Can you explain why the Earth is considered a giant magnet?
- [ ] Can you state the rule for attraction and repulsion of poles?
- [ ] Can you explain single touch and double touch methods of making magnets?
- [ ] Can you list uses of electromagnets in daily life?
- [ ] Can you differentiate between permanent and temporary magnets?
- [ ] Can you define Curie temperature and explain its significance?
- [ ] Can you explain how a magnetic compass works and why its needle aligns north-south?