Summary of HC Verma Solutions Part 2 Chapter 36: Permanent Magnets
FAQs on HC Verma Solutions Class 12 Chapter 36 - Permanent Magnets
1. Where can I find reliable, step-by-step solutions for HC Verma's Class 12 Physics Chapter 36 on Permanent Magnets?
You can find comprehensive and accurate solutions for all exercises in HC Verma's 'Concepts of Physics', Chapter 36 - Permanent Magnets, right here on Vedantu. Our solutions are crafted by subject matter experts to provide a clear, step-by-step methodology for each problem, ensuring they align with the core principles of the CBSE 2025-26 syllabus and help build a strong conceptual foundation for competitive exams.
2. What are the key concepts I need to master from this chapter to solve the HC Verma questions effectively?
To effectively solve the problems in HC Verma Chapter 36, you should focus on understanding these core concepts:
The properties of bar magnets and their magnetic field lines.
Calculation of torque (τ = mB sinθ) and potential energy of a magnetic dipole in a uniform magnetic field.
The distinction between magnetic intensity (H), intensity of magnetisation (M), and magnetic field (B).
The properties of diamagnetic, paramagnetic, and ferromagnetic substances.
The concept of the hysteresis loop, including retentivity and coercivity, and its application to permanent magnets and electromagnets.
3. How do the HC Verma solutions explain the difference between a permanent magnet and an electromagnet?
The solutions clarify that the primary difference lies in the material used and the nature of the magnetic field. A permanent magnet is made from a 'hard' ferromagnetic material (like Alnico or steel) which has high retentivity and high coercivity, allowing it to stay magnetised indefinitely without external power. An electromagnet uses a 'soft' ferromagnetic core (like soft iron) which has low retentivity. It behaves as a magnet only when an electric current flows through a surrounding coil, and its strength can be controlled by varying the current.
4. Why is understanding the hysteresis loop so critical for solving numerical problems on permanent magnets in HC Verma?
The hysteresis loop (or B-H curve) is critical because it graphically represents a material's magnetic memory. For problems related to selecting materials for permanent magnets, the loop's characteristics are key. A wide and tall hysteresis loop indicates high retentivity (strong magnetism remains after the magnetising field is removed) and high coercivity (high resistance to demagnetisation). HC Verma problems often require you to interpret these properties to determine a material's suitability as a permanent magnet.
5. How does one correctly approach the classification of magnetic materials (dia, para, ferro) when solving problems from this chapter?
When solving problems, the classification depends on how a material responds to an external magnetic field, which is determined by its magnetic susceptibility (χ). The correct approach is to remember:
- Diamagnetic materials are feebly repelled by magnets (e.g., copper, bismuth). Their susceptibility is small and negative.
- Paramagnetic materials are feebly attracted by magnets (e.g., aluminium, calcium). Their susceptibility is small and positive.
- Ferromagnetic materials are strongly attracted by magnets (e.g., iron, cobalt, nickel). They have a large, positive susceptibility and exhibit properties like hysteresis.
6. What are the common methods for demagnetising a permanent magnet as per the concepts in this chapter?
The solutions based on HC Verma's text explain three primary methods to demagnetise a permanent magnet, which involves randomising its aligned magnetic domains:
Heating: Heating the magnet above its Curie temperature causes the thermal agitation to overcome the domain alignment, leading to demagnetisation.
Applying a Reverse Magnetic Field: Subjecting the magnet to a reverse magnetic field with a strength equal to or greater than its coercivity will nullify its magnetism.
Mechanical Action: Rough handling, such as hammering or dropping the magnet repeatedly, can disrupt the alignment of the magnetic domains and weaken its field.
7. What is a common mistake students make when calculating the torque on a magnetic dipole in HC Verma exercises?
A very common mistake is confusing the angle (θ) in the torque formula, τ = mB sin(θ). Students sometimes incorrectly use the angle given relative to the plane of the coil instead of the angle between the magnetic dipole moment vector (m) and the magnetic field vector (B). The magnetic moment vector is perpendicular to the plane of a current loop. Always ensure you are using the correct angle between these two vectors for an accurate calculation.
