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Ampere-Turns per Meter: SI Unit of Magnetizing Force (Magnetic Field Intensity)

Ampere-turns per meter (A-turns/m) is the SI unit used to quantify magnetizing force or magnetic field intensity. It represents the magnetomotive force (MMF) per unit length along a magnetic path, such as within a magnetic material or in the vicinity of a current-carrying conductor.

Key Concepts


  • Magnetizing Force (H): Also known as magnetic field intensity, it is the measure of the strength of the magnetic field created by a current-carrying conductor or within a magnetic material.
  • Ampere-Turns per Meter (A-turns/m): The magnetizing force per unit length, calculated as the product of the current (in amperes) and the number of turns per unit length in a coil.


The magnetizing force \(H\) in ampere-turns per meter is given by:
\[ H = \frac{N I}{\ell} \]

  • \( N \) is the number of turns of wire in the coil.
  • is the current in amperes \(A\) flowing through the coil.
  • \( \ell \) is the length of the coil in meters.


Magnetic Materials

  • Magnetic Properties: Ampere-turns per meter is used to define the magnetizing force required to induce a certain magnetic flux density (B) within magnetic materials like iron cores in transformers or inductors.
  • Hysteresis Curve: Helps in determining the magnetization characteristics of materials by plotting the relationship between magnetizing force (H) and magnetic flux density \(B\).


  • Design and Optimization: Engineers use ampere-turns per meter to design and optimize the performance of electromagnets by calculating the required number of turns and current to achieve a desired magnetic field strength.
  • Control of Magnetic Fields: Ensures precise control over magnetic fields in various applications such as magnetic sensors, actuators, and magnetic resonance imaging (MRI) systems.

Example Calculation

Consider a solenoid with the following specifications:

  • Coil length \( \ell = 0.5 \) meters
  • Number of turns \( N = 1000 \)
  • Current \( I = 2 \) amperes

The magnetizing force (H) in the solenoid would be:
\[ H = \frac{N I}{\ell} = \frac{1000 \times 2}{0.5} = 4000 \text{ A-turns/m} \]

This means that within the solenoid, the magnetizing force is 4000 ampere-turns per meter, contributing to the establishment of the magnetic field intensity.

Ampere-turns per meter (A-turns/m) is a fundamental unit in electromagnetism used to quantify magnetizing force or magnetic field intensity. It is essential for understanding and designing magnetic systems and devices, ensuring efficient operation and control of magnetic fields in various industrial and scientific applications. By manipulating ampere-turns per meter, engineers can tailor magnetic fields to meet specific requirements, thereby enhancing the performance and functionality of electromagnetic devices.

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