Define induced magnetism. Also, explain some methods for induced magnetism.

Induced Magnetism:

Induced magnetism refers to the temporary magnetization of a material when it is placed in a magnetic field. When a material that is not normally magnetic (such as a piece of iron or steel) is exposed to a magnetic field, it becomes magnetized and starts to act like a magnet. The magnetization of the material occurs due to the alignment of its atomic magnetic moments in the direction of the applied external magnetic field. This induced magnetism is typically temporary; when the external magnetic field is removed, the material usually loses its magnetization.

Induced magnetism is a key concept in understanding how certain materials respond to magnetic fields, particularly ferromagnetic materials such as iron, cobalt, and nickel.

How Induced Magnetism Works:

  1. Atomic Magnetic Moments: Every atom has electrons, which possess both an orbital motion around the nucleus and an intrinsic property called spin. Both of these properties give rise to a tiny magnetic moment. In most materials, the magnetic moments of individual atoms are oriented randomly, so the material does not exhibit any noticeable magnetism.

  2. Application of External Magnetic Field: When a non-magnetic material (such as iron) is placed in an external magnetic field, the atomic magnetic moments within the material tend to align with the applied field. The alignment of these atomic moments creates a net magnetic moment for the entire material, turning it into a magnet, at least temporarily.

  3. Magnetic Domains: In ferromagnetic materials, the material is divided into regions called magnetic domains. Each domain contains a large number of atoms with their magnetic moments aligned in the same direction. When the external magnetic field is applied, these domains tend to align with the field, causing the material to become magnetized.

  4. Temporary Magnetization: Induced magnetism is typically temporary. When the external magnetic field is removed, the alignment of the atomic moments or domains may be disturbed, causing the material to lose its induced magnetism. However, if the material is a ferromagnet, it may retain some of the magnetization even after the external field is removed, which is known as remanent magnetism.

Methods of Induced Magnetism:

There are several ways to induce magnetism in a material. The methods depend on the type of material and the nature of the external magnetic field. Here are some common methods of inducing magnetism:

1. Placing a Material in a Magnetic Field:

  • The simplest method of inducing magnetism in a material is to place it in an external magnetic field. If the material is ferromagnetic (such as iron), it will become magnetized as the magnetic domains inside the material align with the external field.
  • Example: When a piece of iron is placed near a strong magnet, it becomes magnetized temporarily, with one end becoming a north pole and the other end becoming a south pole.

2. Stroking the Material with a Magnet (Magnetic Induction by Contact):

  • A common method for inducing magnetism is to stroke a ferromagnetic material with a permanent magnet. When a permanent magnet is repeatedly rubbed along the length of a material, such as a piece of iron or steel, the magnetic domains within the material align in the direction of the magnet’s field.
  • This method induces a temporary magnetic effect in the material. If the material is strongly magnetized, it might even become a permanent magnet, depending on its composition.
  • Example: Stroking a needle with a magnet can induce a magnetic moment in the needle, turning it into a temporary magnet.

3. Electromagnetic Induction:

  • When a current-carrying wire is placed near a ferromagnetic material, the magnetic field generated by the current induces magnetism in the material. This is a form of induced magnetism, and it can be amplified by increasing the current or the number of coils around the material.
  • A common example of this method is the creation of electromagnets, where a wire is coiled around a piece of iron or steel, and a current is passed through the wire, inducing a magnetic field in the core. The induced magnetism can be turned on and off by controlling the flow of current.
  • Example: A simple electromagnet can be made by wrapping a coil of wire around a nail and running an electric current through the coil. The nail becomes magnetized while the current is flowing.

4. Using a Coil (Solenoid) to Induce Magnetism:

  • A solenoid is a long coil of wire that produces a uniform magnetic field when an electric current passes through it. If a ferromagnetic material is placed inside a solenoid, the material becomes magnetized due to the magnetic field generated by the solenoid.
  • The induced magnetism in the material is temporary and can be adjusted by changing the strength of the current or the number of turns in the solenoid.
  • Example: Placing a piece of iron inside a solenoid will induce a strong magnetic field in the iron. When the current is turned off, the induced magnetism will disappear unless the material retains some magnetization.

5. Magnetic Induction by Heating (Curie Point):

  • When a ferromagnetic material is heated above a certain temperature known as the Curie point (the material’s specific temperature threshold), the material’s magnetic properties change. At temperatures above the Curie point, the material loses its ferromagnetic properties and becomes paramagnetic, meaning that the domains are no longer aligned, and the material cannot be magnetized.
  • Upon cooling, the material may regain its magnetization if the magnetic field is applied during the cooling process.
  • Example: If a piece of iron is heated to its Curie temperature and then placed in a magnetic field as it cools, it can retain a portion of the magnetization, resulting in induced magnetism.

Types of Materials Involved in Induced Magnetism:

  • Ferromagnetic Materials: These materials (like iron, cobalt, and nickel) are the most easily magnetized by induction because their atomic magnetic moments can align in the direction of the applied field, creating strong induced magnetism.
  • Paramagnetic Materials: These materials (such as aluminum) are weakly attracted to a magnetic field, and their magnetization is very weak and temporary.
  • Diamagnetic Materials: These materials (such as copper or bismuth) develop a very weak opposite magnetization when exposed to an external field, leading to a repulsion.

Related Questions:

  1. Why are the Earth’s geographical and magnetic axes not coincident? Explain.
  2. Define and explain magnetism.
  3. What is the domain theory of magnetism? Explain.
  4. Explain magnetic field strength and magnetic shielding.
  5. Can two magnetic field lines intersect each other? Justify your answer.
  6. A freely suspended magnet always points along the north-south direction. Why?
  7. What is the neutral zone or field-free region of the magnetic field?
  8. Is there any material which does not have any magnetic behavior? Justify your answer.
  9. A proton is also a charged particle and spins like an electron. Why is its effect neglected in the study of magnetism?
  10. What is the geomagnetic reversal phenomenon? Explain.
  11. Why does the Earth spin about its geographical axis instead of its magnetic axis? Explain.
  12. What is the difference between paramagnetic and ferromagnetic materials?
  13. On what factors does the strength of the magnetic field of an electromagnet depend?
  14. Explain the magnetic field of a bar magnet and that of a solenoid, and compare them.
  15. Which part of the study is not handled by the classical study of physics?
  16. Discuss the importance of physics in our daily life.
  17. Briefly discuss the importance of physics in other disciplines of science.
  18. Differentiate the terms ‘science’, ‘technology’, and ‘engineering’ with suitable examples.
  19. Explain the terms hypothesis, theory, and law with examples.
  20. Discuss the role of physics in space exploration.