A bar of diamagnetic substance is placed in a magnetic field with its length making angle `theta` with the direction of the magnetic field. How will the bar behave ?

Options

A. It will align itself perpendicular to the magnetic field
B. It will remain as before
C. It will align itself parallel to the magnetic field
D. Its behaviour cannot be predicted

Answer

To understand how a bar of diamagnetic substance behaves when placed in a magnetic field at an angle θ, we can break down the explanation into several steps:

### Step-by-Step Solution:

1. **Understanding Diamagnetic Materials**:
- Diamagnetic materials are composed of atoms that have no net magnetic moment. This is because all their electron shells are completely filled, resulting in no unpaired electrons.

2. **Behavior in a Magnetic Field**:
- When a diamagnetic material is placed in a magnetic field, it does not have an inherent magnetic moment. However, the presence of the external magnetic field induces a magnetic moment in the material.

3. **Induced Magnetic Field**:
- The induced magnetic moment in a diamagnetic material is in the opposite direction to the applied magnetic field. This means that if the magnetic field is directed in one way, the induced magnetic field within the diamagnetic material will be directed opposite to it.

4. **Resulting Force**:
- Due to the induced magnetic field, the diamagnetic material experiences a repulsive force when placed in the external magnetic field. This repulsion is a result of the interaction between the induced magnetic field and the external magnetic field.

5. **Orientation of the Bar**:
- Because of the repulsive force acting on the diamagnetic bar, it will tend to align itself perpendicular to the direction of the magnetic field. This is due to the fact that the configuration with the least energy is achieved when the bar is perpendicular to the magnetic field lines.

### Conclusion:
- Therefore, when a bar of diamagnetic substance is placed in a magnetic field at an angle θ, it will experience a repulsive force and will tend to orient itself perpendicular to the direction of the magnetic field.

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