A dip circle is taken to geomagnetic equator. The needle is allowed to move in a vertical plane perpendicular to the magnetic meridian. The needle will stay

Options

A. in horizontal direction only
B. in vertical direction only
C. in any direction except vertical and horizontal
D. in any direction it is released.

Answer

To solve the question regarding the behavior of a dip circle needle at the geomagnetic equator, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Dip Circle**: A dip circle is an instrument used to measure the angle of dip of the Earth's magnetic field. It consists of a magnetic needle that can pivot freely.

2. **Location of the Geomagnetic Equator**: The geomagnetic equator is an imaginary line around the Earth where the magnetic field is horizontal. At this location, the magnetic field lines are parallel to the surface of the Earth.

3. **Behavior of the Magnetic Needle**: When the needle of the dip circle is allowed to move, it will align itself with the Earth's magnetic field. Since we are at the geomagnetic equator, the magnetic field is horizontal.

4. **Movement Restrictions**: The problem states that the needle is allowed to move in a vertical plane that is perpendicular to the magnetic meridian. This means that while the needle can pivot, its movement is restricted in the horizontal direction.

5. **Conclusion on Needle's Position**: Given that the magnetic field at the geomagnetic equator is horizontal and the needle is free to move in the vertical plane, the needle will align itself vertically. Therefore, the needle will stay in the vertical direction only.

### Final Answer:
The needle will stay in the vertical direction only (Option B).

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