We can define two planes for a particular location on the surface of earth. One is called magnetic meridian and the other is called geographic meridian. Magnetic meridian for a point on the surface of earth is defined as a plane passing through this point and containing magnetic axis of earth. Similarly geographic meridian for a point on the surface of earth is defined as plane passing through this point and containing geographic axis of rotation. If we draw these two planes for a point on the surface of earth then in general these are found at some angle. Angle between these two planes is called declination for that place. Importance of magnetic meridian at a point is that net magnetic field vector of earth for that point lies on this plane. Usually net magnetic field of earth is inclined at some angle with the horizontal and this angle is called angle of dip for that place.
How many points are there on surface of earth where angle of dip is zero ?

Options

A. 2
B. 4
C. 8
D. infinite

Explanation

To solve the question of how many points on the surface of the Earth have an angle of dip equal to zero, we can follow these steps:

### Step 1: Understand the Definitions
- **Magnetic Meridian**: A plane that passes through a point on the Earth's surface and contains the magnetic axis of the Earth.
- **Geographic Meridian**: A plane that passes through a point on the Earth's surface and contains the geographic axis of rotation.
- **Angle of Dip**: The angle between the magnetic field lines and the horizontal plane. It indicates how much the magnetic field is inclined.

### Step 2: Identify the Concept of Angle of Dip
- The angle of dip is zero when the magnetic field lines are horizontal. This occurs when the magnetic field is aligned with the surface of the Earth.

### Step 3: Locate the Magnetic Equator
- The angle of dip is zero along the **magnetic equator**. At this line, the magnetic field is horizontal, meaning that a magnetic needle would align parallel to the Earth's surface.

### Step 4: Determine the Points with Zero Angle of Dip
- The magnetic equator runs around the Earth, similar to the geographic equator. Therefore, all points along this magnetic equator will have an angle of dip of zero.

### Step 5: Conclusion
- Since the magnetic equator is a continuous line around the Earth, there are infinitely many points on the surface of the Earth where the angle of dip is zero.

### Final Answer
There are infinitely many points on the surface of the Earth where the angle of dip is zero, specifically along the magnetic equator.

---