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 `90^@` ?

Options

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

Explanation

To solve the question regarding how many points on the surface of the Earth have an angle of dip of 90 degrees, we will follow these steps:

### Step 1: Understand the Concept of Angle of Dip
The angle of dip is defined as the angle made by the magnetic field lines with the horizontal plane. When this angle is 90 degrees, it means that the magnetic field lines are vertical.

### Step 2: Identify the Points of Interest
The angle of dip is 90 degrees at specific locations on Earth, which are typically at the magnetic poles. There are two magnetic poles: the Magnetic North Pole and the Magnetic South Pole.

### Step 3: Analyze the Magnetic Field Lines
At the Magnetic North Pole, the magnetic field lines enter the Earth vertically downwards, and at the Magnetic South Pole, they exit vertically upwards. This means that at both poles, the angle of dip is indeed 90 degrees.

### Step 4: Conclusion
Since the angle of dip is 90 degrees at both the Magnetic North Pole and the Magnetic South Pole, we conclude that there are exactly **two points** on the surface of the Earth where the angle of dip is 90 degrees.

### Final Answer
There are **two points** on the surface of the Earth where the angle of dip is 90 degrees.

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