Question

To protect the instrument from magnetic field, it is completely surrounded by ______.

• A. soft ferromagnetic substance.
• B. diamagnetic substance only.
• C. paramagnetic substance only.
• D. both diamagnetic and paramagnetic substances.

Hint:

"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.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Magnetic shielding is a method to redirect magnetic field lines away from a specific region.

Step 2: Formula Application:
Materials with high magnetic permeability ($\mu$) are required to "trap" and guide the magnetic flux lines.

Step 3: Explanation:
Soft ferromagnetic materials (like soft iron) have very high permeability. When an instrument is placed inside a hollow box of such material, the external magnetic field lines prefer to pass through the high-permeability walls rather than the air inside, leaving the interior field-free.

Step 4: Final Answer:
The instrument is protected by surrounding it with a soft ferromagnetic substance.