When the `N`-pole of a bar magnet points towards the south and S-pole towards the north, the null points are at the

Options

A. Magnetic axis
B. Magnetic centre
C. Normal bisector of magnetic axis
D. N and S poles

Answer

To solve the problem, we need to understand the concept of null points in relation to a bar magnet and the Earth's magnetic field.

### Step-by-Step Solution:

1. **Understanding the Setup**:
- We have a bar magnet with its North (N) pole pointing towards the South (S) direction and its South (S) pole pointing towards the North (N) direction.
- This means that the bar magnet is aligned opposite to the Earth's magnetic field.

2. **Magnetic Field of the Bar Magnet**:
- The magnetic field lines of a bar magnet emerge from the North pole and enter the South pole.
- When the bar magnet is placed in the Earth's magnetic field, it creates a combined magnetic field.

3. **Definition of Null Point**:
- A null point is a location where the magnetic field strength is zero. This occurs when the magnetic field of the bar magnet and the Earth's magnetic field cancel each other out.

4. **Analyzing the Magnetic Field Directions**:
- Since the bar magnet's North pole is pointing towards the South, it means that the magnetic field of the bar magnet is directed towards the South.
- The Earth's magnetic field, in the Northern Hemisphere, generally points towards the North.

5. **Finding the Null Point**:
- The null points will be located along the axis of the bar magnet, where the fields can potentially cancel each other out.
- Since the strength of the North and South poles of the magnet is not specified, we cannot determine the exact position of the null point, but we can conclude that it will be along the magnetic axis of the magnet.

6. **Conclusion**:
- Therefore, the null points are located on the axis of the magnet, which means they will be somewhere along the line extending from the North pole to the South pole of the bar magnet.

### Final Answer:
The null points are at the axis of the magnet.

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