Question

Iron loses its magnetic property at (a) boiling point (b) melting point (c) \(1000 \mathrm{~K}\) (d) curie point

Short answer

Iron loses its magnetic property at the Curie point (option d).

Step-by-step solution

Understanding the Question

The question asks about the specific temperature at which iron loses its magnetic property. This is a property of materials related to their magnetic behavior at certain temperatures. We are given four temperatures/points to consider.

Definition of Curie Point

The Curie point, or Curie temperature, is the temperature at which certain materials lose their permanent magnetic properties and become paramagnetic. Iron is one such material.

Comparison with Other Options

The boiling point, melting point, and the specific mentioned temperature of 1000 K are unrelated to the magnetic properties in the context of permanent magnetism. These points are typically where a substance changes its state of matter, i.e., from solid to liquid (melting) or liquid to gas (boiling), which do not inherently affect magnetic properties in a way described by the Curie point.

Confirming the Option

Given that the Curie point is specifically about losing magnetic properties, and since that is the focus of the question, option (d) Curie point is the correct answer. Iron's Curie temperature is around 1043 K, fittingly close to the options related to temperature changes affecting magnetic properties.

Key concepts

Magnetic Properties

Magnetic properties are inherent characteristics of certain materials that determine how they respond to an external magnetic field. These properties are critical in understanding why some substances act as magnets while others do not. Materials can generally be classified into different categories based on their magnetic properties:

• Ferromagnetic: These materials, like iron, nickel, and cobalt, are strongly attracted to magnets and can be magnetized themselves.
• Paramagnetic: These materials are weakly attracted to magnets and do not retain magnetism once the external magnetic field is removed.
• Diamagnetic: These materials are slightly repelled by strong magnets and do not develop magnetism.

Each category is defined by the microscopic interactions between electron spins and magnetic fields. The Curie point is significant for ferromagnetic materials, as it marks the temperature above which these materials lose their strong magnetic properties.

Iron

Iron is one of the most common ferromagnetic materials found in nature. Its strong magnetic properties make it a key component in various technological applications, such as electric motors and transformers. The magnetic behavior of iron is primarily due to its electron configuration. In iron, the spinning electrons line up in a way that their magnetic moments add together, creating a strong overall magnetic field. Upon heating, ferromagnetic materials like iron can lose their ordered electron spin alignment. Above the Curie point, which for iron is around 1043 K, the thermal energy disrupts this alignment. This transition renders the material paramagnetic, meaning iron can no longer maintain a permanent magnetic state without an external magnetic field. The robustness of iron's magnetic properties at room temperature makes it invaluable in everyday use, but understanding its behavior at elevated temperatures is crucial for applications involving heat.

Paramagnetism

Paramagnetism is a form of magnetism that occurs only in the presence of an externally applied magnetic field. In this state, materials such as iron above its Curie point become temporarily magnetized and the magnetization disappears when the external field is removed. This phenomenon arises because, although the individual atomic moments tend to align with the magnetic field, the thermal agitation at high temperatures prevents permanent alignment. In simple terms, paramagnetic materials like iron (above 1043 K) exhibit a weak attraction to magnetic fields and do not sustain this magnetism on their own. Unlike ferromagnetic materials, paramagnetic materials do not retain magnetic properties once the external field ceases to exist. It's essential to recognize that the change from ferromagnetism to paramagnetism is a reversible process. Once the material cools below its Curie point, it can regain its original magnetic properties.