Which of the following is true regarding dimagnetic substances (symbols have their usual meaning)

Options

A. `mu gt 1, chi_(m) gt 1`
B. `mu_(r) gt 1, chi_(m) lt 1`
C. `mu_(r) gt 1, chi_(m) lt 0`
D. `mu lt 1, chi_(m) lt 0`

Explanation

To solve the problem regarding diamagnetic substances, we need to understand the properties of these materials in the context of magnetic fields. Let's break it down step by step.

### Step-by-Step Solution:

1. **Definition of Diamagnetic Substances**:
- Diamagnetic substances are materials that are weakly repelled by a magnetic field. This means that when placed in an external magnetic field, they exhibit a very weak magnetization that is opposite to the direction of the applied field.

2. **Magnetization (I)**:
- The magnetization (I) of a diamagnetic substance is defined as the magnetic moment per unit volume. For diamagnetic materials, this magnetization is small and directed opposite to the applied magnetic field (H).

3. **Susceptibility (χ)**:
- The magnetic susceptibility (χ) is defined as the ratio of the magnetization (I) to the strength of the magnetic field (H):
\[ \chi = \frac{I}{H} \]
- Since I is opposite to H and has a small magnitude, the susceptibility for diamagnetic substances is slightly negative, indicating that they are repelled by the magnetic field.

4. **Permeability (μ)**:
- The permeability (μ) of a material is related to its susceptibility by the equation:
\[ \mu = 1 + \chi \]
- Given that the susceptibility (χ) is slightly negative for diamagnetic substances, the relative permeability (μ) will be less than 1:
\[ \mu < 1 \]

5. **Conclusion**:
- Based on the properties of diamagnetic substances, we can conclude that the correct statement regarding them is that their relative permeability is less than 1.

### Final Answer:
The correct option regarding diamagnetic substances is that their relative permeability (μ) is less than 1.

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