The Earth S Magnetism

Step 1: Understanding the Concept:
This question asks for the definition of one of the elements of Earth's magnetic field, which are used to describe the field at any point on the Earth's surface.
Step 2: Detailed Explanation:
Let's define the key terms:
- Geographical Meridian: An imaginary vertical plane passing through a point on the Earth's surface and the Earth's axis of rotation (i.e., passing through the geographic North and South poles). It defines the direction of true north.
- Magnetic Meridian: An imaginary vertical plane at a point on the Earth's surface which contains the direction of the horizontal component of the Earth's magnetic field. A freely suspended compass needle aligns itself in this plane. It defines the direction of magnetic north.
- Angle of Declination ( ): The angle between the geographical meridian and the magnetic meridian at a place. It is the angle by which a compass needle deviates from true north.
- Angle of Dip ( ): The angle between the direction of the Earth's total magnetic field and the horizontal direction in the magnetic meridian.
The question asks for the angle between the magnetic meridian and the geographical meridian, which is the definition of the angle of declination.
Step 3: Final Answer:
The angle between the magnetic meridian and geographical meridian is called declination. Therefore, option (B) is correct.