Which of the following materials would weaken the magnetic field strength at a point if introduced ?

Options

A. Cu
B. Al
C. Liquid `O_(2)`
D. Co

Answer

To determine which material would weaken the magnetic field strength at a point if introduced, we need to analyze the magnetic properties of the given materials: copper, aluminum, liquid oxygen, and cobalt.

### Step-by-Step Solution:

1. **Identify the Types of Materials:**
- Copper: This is a **diamagnetic** material.
- Aluminum: This is a **paramagnetic** material.
- Liquid Oxygen: This is also a **paramagnetic** material.
- Cobalt: This is a **ferromagnetic** material.

2. **Understand Magnetic Properties:**
- **Diamagnetic Materials**: These materials have a very weak and negative susceptibility to magnetic fields. They create an opposing magnetic field when exposed to an external magnetic field, which can weaken the overall magnetic field strength.
- **Paramagnetic Materials**: These materials have a small positive susceptibility to magnetic fields. They are weakly attracted to magnetic fields and do not significantly weaken the magnetic field.
- **Ferromagnetic Materials**: These materials have a strong positive susceptibility and can enhance the magnetic field strength due to their strong magnetization.

3. **Compare the Materials:**
- Since diamagnetic materials (like copper) create an opposing magnetic field, they will weaken the magnetic field strength when introduced.
- Paramagnetic materials (like aluminum and liquid oxygen) will not weaken the magnetic field significantly; they may even slightly enhance it.
- Ferromagnetic materials (like cobalt) will enhance the magnetic field strength due to their strong magnetization.

4. **Conclusion:**
- Among the given options, **copper**, being a diamagnetic material, would weaken the magnetic field strength at a point if introduced.

### Final Answer:
**Copper** is the material that would weaken the magnetic field strength at a point if introduced.

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