The variation of the intensity of magnetisation (l) with respect to the magnetising field (H) in a diamagnetic substance is described by the graph.

Options

A. OC
B. OD
C. OA
D. OB

Answer

To solve the problem regarding the variation of the intensity of magnetization (I) with respect to the magnetizing field (H) in a diamagnetic substance, we can follow these steps:

### Step 1: Understand the Relationship
The intensity of magnetization (I) in a diamagnetic material is related to the magnetizing field (H) through the equation:
\[ I = \chi H \]
where \( \chi \) is the magnetic susceptibility of the material. For diamagnetic substances, \( \chi \) is negative and has a very small magnitude.

### Step 2: Analyze the Graph
In the graph provided, we need to identify the regions where the intensity of magnetization (I) is plotted against the magnetizing field (H). The graph will show a linear relationship, but since it is a diamagnetic substance, the slope will be negative.

### Step 3: Identify Key Points
From the graph, identify the points that represent the relationship:
- Points A and B are in the positive region of the graph.
- Points C and D are in the negative region of the graph.

### Step 4: Determine the Slope
The slope of the line in the graph represents the magnetic susceptibility (\( \chi \)). Since we are dealing with a diamagnetic substance, the slope will be negative and very small in magnitude.

### Step 5: Compare Slopes
Among the points identified, we need to find the line segment that has the smallest negative slope. This will be the segment with the least steepness in the negative direction.

### Step 6: Conclusion
From the analysis, we find that the line segment from point O to point C has the smallest negative slope, indicating the least susceptibility in the negative direction. Thus, the correct answer to the question is option A, which corresponds to the line segment OC.

### Summary of the Solution
- The relationship between I and H is linear and negative for diamagnetic substances.
- The slope indicates the magnetic susceptibility, which is negative and small.
- The line segment OC has the smallest slope, confirming it as the correct answer.