Question:
To protect the instrument from magnetic field, it is completely surrounded by ______.
To protect the instrument from magnetic field, it is completely surrounded by ______.
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"Soft" iron is specifically chosen over "hard" iron because it has a narrow hysteresis loop, meaning it does not become permanently magnetized itself, which would otherwise defeat the purpose of the shield.
Updated On: Aug 19, 2026
- soft ferromagnetic substance.
- diamagnetic substance only.
- paramagnetic substance only.
- both diamagnetic and paramagnetic substances.
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The Correct Option is A
Solution and Explanation
Step 1: Understanding the Question:
The question refers to the concept of "Magnetic Shielding"—the practice of protecting sensitive electrical instruments from stray external magnetic fields.
Step 2: Detailed Explanation:
Magnetic shielding utilizes materials with a very high magnetic permeability ($\mu$).
When a highly permeable material is placed in a magnetic field, the magnetic field lines strongly prefer to travel through the material rather than through the surrounding air or free space.
Soft ferromagnetic materials (like soft iron or mu-metal) have extremely high permeability. If an instrument is enclosed within a hollow cylinder or box made of soft iron, the external magnetic lines will wrap around the shell through the metal, leaving the interior cavity virtually field-free.
Diamagnetic and paramagnetic substances have permeabilities too close to that of free space ($\mu_r \approx 1$) to effectively redirect field lines.
Step 3: Final Answer:
The instrument should be surrounded by a soft ferromagnetic substance, matching option (a).
The question refers to the concept of "Magnetic Shielding"—the practice of protecting sensitive electrical instruments from stray external magnetic fields.
Step 2: Detailed Explanation:
Magnetic shielding utilizes materials with a very high magnetic permeability ($\mu$).
When a highly permeable material is placed in a magnetic field, the magnetic field lines strongly prefer to travel through the material rather than through the surrounding air or free space.
Soft ferromagnetic materials (like soft iron or mu-metal) have extremely high permeability. If an instrument is enclosed within a hollow cylinder or box made of soft iron, the external magnetic lines will wrap around the shell through the metal, leaving the interior cavity virtually field-free.
Diamagnetic and paramagnetic substances have permeabilities too close to that of free space ($\mu_r \approx 1$) to effectively redirect field lines.
Step 3: Final Answer:
The instrument should be surrounded by a soft ferromagnetic substance, matching option (a).
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