Difference Between Magnetization and Magnetic Intensity with Examples
Magnetic Intensity and Magnetisation are important physical quantities that help describe magnetic effects in various substances. These concepts are crucial for understanding how materials behave in the presence of magnetic fields and are foundational for topics in electricity and magnetism.
Magnetic Intensity and Magnetisation: Fundamental Concepts
A magnet exerts attractive or repulsive forces on other objects, especially metallic substances. This property, known as magnetism, results from the alignment and interaction of atomic-level magnetic dipoles inside the material.
Magnetisation is a measure of the magnetic dipole moment induced or present in a given material per unit volume. It reveals how strongly a substance is magnetised when placed near a magnet or inside a magnetic field.
The effect of magnetism can also be produced by passing an electric current through a wire or coil, due to the motion and spin of electrons within atoms. The magnitude of the force on any charged particle in a magnetic field depends on the charge, velocity, and field strength.
Source of Magnetisation
Magnetisation in materials arises from the movement of electrons (orbital motion) and their intrinsic spin. In the presence of an external magnetic field, the atomic dipoles tend to align, producing a net magnetic moment.
The resulting magnetisation is a vector quantity. It is key in identifying and classifying materials based on their response in a magnetic field. Substances like iron, nickel, and cobalt show strong magnetisation, while others like copper show weak or negative magnetisation.
Magnetisation Formula and Explanation
The intensity of magnetisation (commonly denoted as M) can be mathematically expressed as the net magnetic moment per unit volume:
M = mnet / V
Here, mnet is the net magnetic moment and V is the volume. The SI unit of magnetisation is ampere per meter (A/m).
In solenoids, which are coils with n turns per unit length, carrying a current I, the initial magnetic field inside (no core material) is:
B0 = μ0 n I
Where μ0 is the permeability of free space.
When a magnetic material is placed inside the solenoid, the total magnetic field becomes:
B = B0 + Bm
Bm = μ0M
Therefore, the total field inside the material:
B = μ0(H + M)
Here, H is magnetic intensity (also called magnetising field) and M is magnetisation. H is determined by external causes (like current in the solenoid), while M is due to the material’s property.
Magnetic Intensity: Definition and Formula
Magnetic intensity (denoted as H) is the vector quantity that represents the strength of the magnetising field at a particular location, independent of how the material actually responds.
The formula relating B, M, and H is:
H = B/μ0 - M
Alternatively, B = μ0(H + M) provides the total magnetic field inside the material.
Role of Magnetic Susceptibility (χ)
Magnetic susceptibility (χ) characterises how a material responds to an external magnetic field. It is defined by:
M = χH
- Paramagnetic materials: small, positive χ
- Diamagnetic materials: small, negative χ
- Ferromagnetic materials: large, positive χ
Using χ, the total field can be written as:
B = μ0(1 + χ)H = μ0μrH = μH
Where μr is the relative permeability of the material.
Physical Meaning and Practical Example
When a ferromagnetic material like iron is placed in a strong external field, its atomic dipoles align with the field, leading to strong magnetisation. The magnetic intensity (H) is due to the external field, whereas magnetisation (M) arises from the internal alignment of dipoles.
For example, placing an iron rod inside a solenoid increases the total field inside because M adds to H, resulting in a stronger B.
| Parameter | Magnetisation (M) | Magnetic Intensity (H) |
|---|---|---|
| Definition | Net magnetic moment per unit volume of material | Strength of the externally applied magnetic field |
| Origin | Alignment of atomic dipoles/internal response | Current or other external factors |
| SI Unit | A/m | A/m |
| Depends on | Material’s nature and external field | Applied current, number of turns in coil |
Step-by-Step Approach to Solve Problems
- Find the net magnetic moment (mnet) and volume (V) of the material.
- Compute magnetisation (M = mnet/V).
- If given a solenoid or coil, use B0 = μ0 n I to get the basic field.
- If material’s magnetisation is involved, use B = μ0(H + M) to get total field.
- If magnetic susceptibility is given, relate M and H by M = χH.
| Concept | Formula | Unit | Meaning |
|---|---|---|---|
| Magnetisation (M) | M = mnet / V | A/m | Magnetic moment per unit volume |
| Magnetic field (B) | B = μ0(H + M) | Tesla (T) | Total field inside the material |
| Magnetic intensity (H) | H = B/μ0 - M | A/m | External cause of field |
| Magnetic susceptibility (χ) | M = χH | (dimensionless) | Material’s response to field |
Example
Suppose a material has a total magnetic moment of 2 × 10-3 A·m2 and a volume of 5 × 10-5 m3. A magnetic field with intensity H = 300 A/m is applied. Find the magnetisation and total magnetic field inside (if μ0 = 4π × 10-7 T·m/A).
M = (2 × 10-3) / (5 × 10-5) = 40 A/m
B = μ0(H + M) = 4π × 10-7 × (300 + 40) = 4π × 10-7 × 340 = 4.27 × 10-4 T
To learn more about magnetisation, types of magnetic materials, and detailed applications, visit:
Use these links for solved examples, quizzes, and in-depth concept explanations for better exam preparation.FAQs on Magnetization vs Magnetic Intensity: Complete Guide for Class 12, JEE & NEET
1. What is magnetic intensity?
Magnetic intensity (also called magnetising field, symbol H) is the measure of the strength of an external magnetic field applied to a material. It is defined as the amount of magnetising force per unit length. The SI unit is ampere per meter (A/m).
2. What is magnetization?
Magnetization (M) or magnetic polarization is the net magnetic moment per unit volume of a material. It represents how strongly a material becomes magnetized when placed in an external magnetic field. The SI unit is ampere per meter (A/m).
3. What is the formula for magnetization?
Magnetization (M) is calculated using the formula:
M = m / V,
where m = total magnetic moment, and V = volume of the material. This formula expresses the magnetic moment per unit volume.
4. What is the relation between B, H, and M?
The magnetic field (B), magnetic intensity (H), and magnetization (M) are related by:
B = μ₀ (H + M),
where μ₀ is the permeability of free space. This equation shows that the total magnetic field inside a material is the sum of the field due to the external source (H) and the material's response (M).
5. What is the SI unit of magnetic intensity?
The SI unit of magnetic intensity (H) is ampere per meter (A/m). Both magnetic intensity and magnetization share the same SI unit.
6. Is magnetization the same as magnetic intensity?
No, magnetization and magnetic intensity are different:
- Magnetization (M): Measures the material's response; magnetic moment per unit volume.
- Magnetic intensity (H): Refers to the externally applied magnetic field strength.
7. What is magnetic susceptibility?
Magnetic susceptibility (χm) is a dimensionless quantity that indicates how easily a material is magnetized by an external magnetic field. It is given by:
χm = M / H.
A large χm means the material gets strongly magnetized.
8. What is the difference between magnetization and magnetic intensity?
Magnetization (M) is the net magnetic moment per unit volume and shows the response of a material to an applied field. Magnetic intensity (H) is the measure of the strength of the external magnetizing field applied to the material. Magnetization describes the effect, while magnetic intensity describes the cause.
9. How do you calculate the magnetic field inside a solenoid with a magnetic material core?
The total magnetic field (B) inside a solenoid filled with magnetic material is:
B = μ₀ (H + M).
Here, H is calculated as H = nI (n = number of turns per unit length, I = current), and M is determined by the material's magnetization.
10. What are the physical meanings of H and M?
H (Magnetic intensity): The externally applied field that tries to align the magnetic domains inside a material.
M (Magnetization): The result of this alignment; shows how many domains are aligned and how strongly the material is magnetized.
11. Can magnetic intensity exist without magnetization?
Yes, magnetic intensity (H) can exist even when magnetization (M) is zero. This occurs in a vacuum or in materials that do not get magnetized by applied fields (such as some diamagnetic substances). Magnetization only appears when a material responds to the applied field.
12. What factors affect the magnetization of a material?
Magnetization (M) depends on:
- The type of material (paramagnetic, diamagnetic, ferromagnetic, etc.)
- Strength of the applied magnetic intensity (H)
- Temperature (higher temperature can reduce magnetization for most materials)
- The history of the applied field (magnetic hysteresis in ferromagnets)
