To shield an instrument from external magnetic field, it is placed inside a cabin made of

Options

A. Wood
B. Plastic
C. Diamagnetic substances
D. Iron

Answer

To solve the question of what material should be used to shield an instrument from an external magnetic field, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Magnetic Shielding**:
Magnetic shielding is the process of reducing the magnetic field in a specified area by blocking the field with a barrier made of a magnetic material.

2. **Identify the Properties of Materials**:
Different materials respond differently to magnetic fields.
- **Wood and Plastic**: These materials are non-magnetic and do not provide effective shielding against magnetic fields.
- **Diamagnetic Substances**: These materials have a very weak negative susceptibility to magnetic fields, which means they can slightly repel magnetic fields but are not effective for shielding.
- **Ferromagnetic Substances (like Iron)**: These materials have a high positive susceptibility, meaning they can attract and concentrate magnetic field lines.

3. **Choose the Best Material for Shielding**:
Since we want to shield the instrument from an external magnetic field, we need a material that can effectively redirect or absorb the magnetic field lines. Among the options given, iron is a ferromagnetic material that can effectively shield against external magnetic fields.

4. **Conclusion**:
Therefore, to shield an instrument from an external magnetic field, it should be placed inside a cabin made of **iron**.

### Final Answer:
To shield an instrument from an external magnetic field, it is placed inside a cabin made of **iron**.

---