Magnetism of a bar magnet can be destroyed if it is I. kept in the magnetic meridian. II. placed in a direction opposite to that of the Earth’s horizontal intensity. III. heated to a temperature known as Curie temperature. Select the correct answer using the code given below

1. Fundamentals of Magnets and Magnetic Domains (basic)

To understand a magnet, we must look deep inside its structure. At the microscopic level, materials like iron, nickel, and cobalt consist of tiny regions called magnetic domains. You can think of these as small "neighborhoods" where all the atoms have their individual magnetic moments pointing in the exact same direction. In an ordinary, unmagnetized piece of iron, these neighborhoods are disorganized and point in random directions, effectively canceling each other out. However, in a permanent magnet, these domains are "marching in step," aligned in a uniform direction. This collective alignment is what creates the external magnetic force we observe.

The space around a magnet where this force can be detected is known as the magnetic field Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.196. We visualize this field using field lines, which represent the path a north pole would follow. These lines have specific characteristics: they are continuous closed loops, exiting from the North pole and entering the South pole externally, while traveling from South to North inside the magnet Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.197. A magnet can exert force on another magnet even without touching it, a phenomenon you can see when two like poles repel each other or unlike poles attract Science, Class VIII (NCERT Revised ed 2025), Exploring Forces, p.69.

State of Material	Domain Arrangement	Resulting Magnetic Property
Unmagnetized Iron	Randomly oriented domains	No net magnetic field; no attraction/repulsion.
Permanent Magnet	Aligned domains	Strong net magnetic field with distinct North and South poles.

Because magnetism depends on this delicate internal alignment, it is not permanent in the face of extreme conditions. If you provide enough energy to the system—for example, through heating or physical impact—the atoms begin to vibrate violently. This thermal or kinetic energy overcomes the forces holding the domains in place, causing them to fall out of alignment and return to a random state, thereby destroying the magnet's power. Similarly, placing a magnet in a strong opposing external magnetic field can force these domains to flip or scramble, leading to demagnetization.

Sources: Science, Class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.196-197; Science, Class VIII (NCERT Revised ed 2025), Exploring Forces, p.69

2. Classification of Magnetic Materials (intermediate)

To understand the Classification of Magnetic Materials, we must first look at how substances respond when placed in an external magnetic field. Every material is composed of atoms, but not all atoms behave the same way in the presence of a magnet. Based on their magnetic sensitivity and the alignment of their internal magnetic moments, we classify materials into three primary categories: Diamagnetic, Paramagnetic, and Ferromagnetic.

Diamagnetic substances are the "magnetically shy" materials. When placed in a magnetic field, they develop a very weak magnetism in the opposite direction of the field. This causes them to be weakly repelled by magnets. Examples include water, copper, and bismuth. On the other hand, Paramagnetic substances are weakly attracted. They have permanent atomic magnetic moments that align slightly with an external field, but this alignment is easily disrupted by thermal agitation. Common examples include aluminum and oxygen.

The most significant for our study are Ferromagnetic substances, such as iron, cobalt, and nickel. In these materials, atoms group together in regions called magnetic domains where all magnetic moments are aligned in the same direction even without an external field. As noted in Science, Class VIII, Nature of Matter, p.126, a magnet can easily separate iron from a mixture because of these strong magnetic properties. However, this alignment is not permanent if the environment changes. If you heat a ferromagnet, the thermal energy increases the vibration of atoms, eventually breaking the domain alignment. The specific temperature at which a ferromagnetic material loses its permanent magnetism and becomes paramagnetic is known as the Curie Temperature.

Property	Diamagnetic	Paramagnetic	Ferromagnetic
Effect of Magnet	Weakly Repelled	Weakly Attracted	Strongly Attracted
Field Alignment	Opposite to field	With the field	Strongly with the field
Examples	Copper, Water, Gold	Aluminum, Magnesium	Iron, Nickel, Cobalt

It is also vital to distinguish between physical mixtures and chemical compounds. In a mixture, like iron filings and sulfur, the iron retains its ferromagnetic property and can be extracted with a magnet Science, Class VIII, Nature of Matter, p.128. However, once they react chemically to form a compound (Iron Sulfide), the magnetic properties of the individual elements are lost because the electronic structure has changed.

Sources: Science, Class VIII (NCERT 2025), Nature of Matter: Elements, Compounds, and Mixtures, p.126; Science, Class VIII (NCERT 2025), Nature of Matter: Elements, Compounds, and Mixtures, p.128

3. Components of Earth’s Magnetic Field (intermediate)

To understand the Earth's magnetic field at any specific location, we must look beyond a simple compass needle. Because the Earth's magnetic field is a vector in three-dimensional space, we define it using three specific quantities known as the magnetic elements. Before we dive into them, we must distinguish between two vertical planes: the Geographical Meridian (the plane containing the Earth's axis of rotation) and the Magnetic Meridian (the plane containing the magnetic axis). As noted in Physical Geography by PMF IAS, Earths Magnetic Field (Geomagnetic Field), p.72, the magnetic axis is currently tilted at about 11° relative to the rotational axis, meaning these two planes rarely overlap.

The three components that fully describe the magnetic field at a point are:

• Magnetic Declination (θ): This is the horizontal angle between the geographic north and the magnetic north. When you use a map, you must account for this 'error' to find true north.
• Magnetic Inclination or Dip (δ): This is the angle that the total magnetic field vector makes with the horizontal line at that point. If you were at the magnetic equator, the needle would be perfectly horizontal (0° dip), but at the magnetic poles, the needle would point straight down (90° dip).
• Horizontal Component (Bₕ): Since the total magnetic field (B) often points into or out of the ground, we calculate the part of the force acting horizontally using the formula: Bₕ = B cos(δ).

Understanding these components is also vital for maintaining the health of permanent magnets. For instance, keeping a bar magnet aligned within the magnetic meridian actually helps preserve its magnetism because it stays in harmony with the Earth's natural field lines. Conversely, magnetism can be destroyed by heating a material to its Curie temperature—the point where thermal energy disrupts the alignment of magnetic domains—or by placing it in a direction opposite to the Earth’s horizontal magnetic intensity, which forces a magnetic reversal Physical Geography by PMF IAS, Earths Magnetic Field (Geomagnetic Field), p.74.

Sources: Physical Geography by PMF IAS, Earths Magnetic Field (Geomagnetic Field), p.72; Physical Geography by PMF IAS, Earths Magnetic Field (Geomagnetic Field), p.74

4. Electromagnetism and Hysteresis (exam-level)

To understand the stability of magnets, we must first look at the microscopic level. In materials like iron, atoms act like tiny magnets that cluster into regions called magnetic domains. When these domains are aligned in the same direction, the material becomes a magnet. However, this alignment is not always permanent. As we explore the relationship between electricity and magnetism, we see that magnetic fields are generated by moving charges—whether in a wire or the spinning electrons within an atom Science, class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.201.

The process of demagnetization (destroying a magnet's strength) occurs when these domains are forced out of alignment. One primary method is through thermal agitation. When a magnet is heated, the atoms gain kinetic energy and vibrate violently. At a specific point known as the Curie Temperature, the thermal energy completely overcomes the forces holding the domains in alignment, causing the material to lose its permanent magnetism and behave as a paramagnetic material.

Another critical concept is Magnetic Hysteresis, which describes how the magnetism of a material 'lags' behind the external magnetic force applied to it. This leads to two vital properties:

• Retentivity: The magnetism that remains in a material after the external field is removed.
• Coercivity (Coercive Force): The intensity of an opposing magnetic field required to reduce the material's magnetism to zero.

Therefore, placing a magnet in a strong field directed opposite to its own orientation—such as opposing the Earth's horizontal magnetic intensity—can neutralize its magnetism through this coercive force. Conversely, keeping a magnet aligned with the magnetic meridian (the direction of Earth's natural magnetic field lines) actually helps maintain its orientation and prevents demagnetization Science, class VIII (NCERT 2025 ed.), Exploring Forces, p.69.

Sources: Science, class X (NCERT 2025 ed.), Magnetic Effects of Electric Current, p.201; Science, class VIII (NCERT 2025 ed.), Exploring Forces, p.69

5. Methods of Magnetization and Demagnetization (intermediate)

To understand how we create or destroy magnets, we must first look at the Magnetic Domains within a material. In an ordinary piece of iron, these tiny atomic-level magnets point in random directions, cancelling each other out. Magnetization is the process of forcing these domains into a single, unified alignment, while Demagnetization is the process of scrambling them back into chaos.

There are several ways to achieve Magnetization. While older mechanical methods involved 'stroking' an iron bar with a permanent magnet, the most efficient modern method is Electrical Magnetization. By placing a ferromagnetic material (like an iron nail) inside a solenoid—a coil of many circular turns of insulated copper wire—the strong, uniform magnetic field created by the electric current forces the material's domains to align Science, Class X (NCERT 2025), Magnetic Effects of Electric Current, p.201. This creates an electromagnet, which remains magnetic as long as the current flows Science, Class VIII (NCERT 2025), Electricity: Magnetic and Heating Effects, p.50.

Conversely, Demagnetization occurs when the energy provided to the magnet is enough to overcome the internal forces holding the domains in place. This can happen through three primary methods:

Method	Mechanism
Thermal (Heating)	Heating a magnet to its Curie Temperature provides thermal energy that disrupts domain alignment, turning it into a non-magnetic (paramagnetic) state.
Mechanical Stress	Rough handling, such as repeated hammering or dropping a magnet from a height, physically jars the domains out of alignment.
Opposing Fields	Exposing a magnet to a strong external magnetic field in the opposite direction (or using an alternating current) can force the domains to flip or scramble.

Interestingly, preserving a magnet requires the opposite approach: keeping a magnet aligned with the magnetic meridian (Earth's natural field lines) actually helps maintain its orientation rather than destroying it. Only by fighting against the natural field or applying external energy can magnetism be effectively neutralized.

Sources: Science, Class X (NCERT 2025), Magnetic Effects of Electric Current, p.201; Science, Class VIII (NCERT 2025), Electricity: Magnetic and Heating Effects, p.50

6. The Curie Temperature and Phase Transitions (exam-level)

To understand the Curie Temperature, we must first look at what makes a magnet work at the atomic level. In materials like iron, nickel, or cobalt, atoms act like tiny microscopic magnets. In a permanent magnet, these atomic magnets are aligned in the same direction within regions called magnetic domains. This alignment is maintained by a quantum force known as the exchange interaction, which acts like a "glue" keeping the magnetic moments locked together. Science, Class VIII NCERT, Nature of Matter, p.126 highlights how magnets interact with matter, but the internal stability of that magnetism depends entirely on temperature.

As we heat a magnet, we are essentially injecting thermal energy into the system. Just as heat causes molecules in a liquid to move faster and expand—a principle used in thermometers Certificate Physical and Human Geography, Weather, p.117—it also causes the atoms in a magnet to vibrate more violently. When the temperature reaches a specific critical point known as the Curie Temperature (T꜀), the thermal agitation becomes strong enough to overcome the internal "glue" of the exchange interaction. At this exact moment, the material undergoes a phase transition: it shifts from being ferromagnetic (ordered and strongly magnetic) to paramagnetic (disordered and weakly magnetic). This transition is sudden and effectively destroys the material's permanent magnetism.

This concept is crucial in Earth Sciences. For instance, while the Earth's core is primarily made of iron, scientists have determined its temperature to be approximately 6000°C Physical Geography by PMF IAS, Earth's Interior, p.56. Since the Curie temperature of iron is only about 770°C, the iron in the Earth's core cannot be a "permanent magnet." Instead, Earth's magnetic field must be generated by the movement of molten metal (the dynamo effect) rather than static, permanent magnetism. Just as social structures undergo a "transition" over time Geography of India, Cultural Setting, p.63, magnetic materials undergo a physical transition that fundamentally alters their behavior when environmental thresholds are crossed.

Feature	Below Curie Temperature	Above Curie Temperature
Magnetic State	Ferromagnetic (Permanent)	Paramagnetic (Temporary/Weak)
Atomic Alignment	Ordered/Aligned	Randomized/Disordered
External Field Response	Remains magnetized when field is removed	Loses magnetism when field is removed

Sources: Science, Class VIII NCERT, Nature of Matter, p.126; Certificate Physical and Human Geography, Weather, p.117; Physical Geography by PMF IAS, Earth's Interior, p.56; Geography of India, Cultural Setting, p.63

7. Solving the Original PYQ (exam-level)

This question brings together your understanding of domain theory and the influence of external forces on ferromagnetic materials. To "destroy" magnetism, one must disrupt the orderly alignment of microscopic internal domains. As you learned in the module on thermal properties, Statement III is a definitive method for demagnetization; reaching the Curie temperature provides enough thermal energy to overcome the forces holding domains in place, causing a transition from ferromagnetic to paramagnetic behavior. This effectively scrambles the alignment that makes a bar magnet "permanent."

When considering the Earth's magnetic field, the direction of placement is critical. Statement II is correct because placing a magnet in a direction opposite to the Earth’s horizontal intensity subjects the domains to a coercive force. This external field works against the magnet’s internal alignment, eventually leading to magnetic reversal or the randomization of domains. However, Statement I is a classic UPSC trap. The magnetic meridian represents the natural plane of the Earth's magnetic field lines; keeping a magnet aligned within this meridian actually preserves its orientation by reinforcing the existing domain structure rather than disrupting it.

By applying the logic of thermal agitation and opposing field intensity, we can confidently conclude that only II and III are valid methods for destroying magnetism. Therefore, the correct answer is (C) II and III only. Always remember: magnetism is a state of order, so anything that promotes disorder (heat) or conflict (opposing fields) will destroy it, while alignment with natural fields (the meridian) maintains it. Reference: Physical Geography by PMF IAS.