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Difficulty: MediumMagnetism Fundamentals

When an unmagnetized ferromagnetic bar is exposed to an external magnetic field, which of the following processes causes the bar to become magnetized?

  1. A
    Free valence electrons are permanently stripped away, transforming the metal into an electrical insulator.
  2. B
    The internal magnetic dipoles repel adjacent atoms until all internal poles reverse and cancel out.
  3. The randomly oriented magnetic domains rotate and align in the direction of the external field.Answer
  4. D
    The applied magnetic energy is converted into static electric charge stored across internal dielectric layers.

Answer

The randomly oriented magnetic domains rotate and align in the direction of the external field.
In an unmagnetized ferromagnetic substance, microscopic groups of atoms called magnetic domains have their individual magnetic moments oriented in random directions, canceling each other out. When placed in an external magnetic field, these domains rotate and align parallel to the external field lines, giving the material an overall net magnetic polarity.

Step-by-Step Solution

1
Recall the microscopic structure of unmagnetized ferromagnetic materials.
Unmagnetized ferromagnetic materials consist of microscopic regions called magnetic domains, where magnetic dipoles are grouped but oriented in random directions, resulting in zero net magnetic field.
Understanding domain theory is essential for explaining how materials become magnetized.
2
Analyze the effect of an external magnetic field on these domains.
The external magnetic force exerts a torque on the individual domains, causing them to rotate and align parallel to the external magnetic flux lines.
Alignment of internal domains creates additive magnetic fields that produce distinct north and south poles in the material.

Key Concept

Magnetic domain theory and alignment in ferromagnetic materials
Estimated Time:45s
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Topics

Magnetism Fundamentals

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