(B) Earth's rotation Explanation: Earth's magnetic field is primarily generated by the movement of molten iron in the outer core. This movement, driven by Earth's rotation, creates electric currents, which in turn generate the magnetic field.

(D) Magnetic poles Explanation : The region where the Earth's magnetic field lines converge and enter or exit the Earth's surface is known as the magnetic poles. There are two magnetic poles: the North Magnetic Pole and the South Magnetic Pole.

(D) Aluminium foil Explanation : Aluminium foil is not commonly used in the construction of a magnetometer. Magnetometers are devices used to measure the strength and direction of magnetic fields. Common materials used in magnetometers include barium ferrite, superconducting wire, and fluxgate sensors.

(C) Tesla Explanation : The strength of a magnetic field is measured in teslas (T). One tesla is a very strong magnetic field, so smaller units like millitesla (mT) or microtesla (µT) are often used for practical measurements.

(C) Magnetic reversal Explanation : Magnetic reversal refers to the phenomenon where the Earth's magnetic field periodically reverses its direction over geological time. This means that the North and South Magnetic Poles switch places. These reversals have occurred numerous times throughout Earth's history.

(D) 90 degrees Explanation : At the magnetic poles, the Earth's magnetic field lines are perpendicular to the Earth's surface, resulting in an inclination angle of 90 degrees.

(A) Palaeomagnetism Explanation : Palaeomagnetism is the study of the Earth's ancient magnetic field preserved in rocks. By analysing the magnetization of rocks, scientists can reconstruct the history of the Earth's magnetic field and its changes over time.

(A) Molten iron in the outer core Explanation : The primary source of Earth's magnetic field is the movement of molten iron in the outer core. This convective motion, driven by heat from the core and Earth's rotation, generates electric currents that produce the magnetic field.

(D) Outer core-inner core boundary Explanation : The boundary between the outer core and the inner core of the Earth, known as the outer core-inner core boundary, is where the Earth's magnetic field is generated. The specific process involves the interaction of the liquid iron in the outer core with the solid inner core.

(B) Magnetometer Explanation : Magnetometers are commonly used to measure changes in the Earth's magnetic field. They can detect even small variations in magnetic field strength and direction, making them useful for studying geomagnetic activity, navigation, and geophysical research.

(B) Isogonic line Explanation : The line connecting points on the Earth's surface where the magnetic field is horizontal is called the isogonic line. It represents the locations where the magnetic declination (the angle between true north and magnetic north) is the same.

(C) Magnetic declination Explanation : Magnetic declination refers to the deviation between true north and magnetic north. It represents the angle between the direction of the Earth's magnetic field and the direction towards the geographic north pole.

(C) Magnetometer Explanation : A magnetometer is an instrument used to measure the strength and direction of the Earth's magnetic field. It is commonly used in various fields such as geophysics, navigation, and scientific research.

(A) Magnetopause Explanation : The magnetopause is the boundary region between the Earth's magnetosphere and the solar wind. It is the point where the pressure from the solar wind is balanced by the Earth's magnetic field.

(A) Solar wind particles interacting with the magnetosphere Explanation : The auroras, also known as the Northern Lights (Aurora Borealis) and Southern Lights (Aurora Australis), are caused by charged particles from the solar wind interacting with the Earth's magnetosphere and entering the atmosphere near the poles.

Geomagnetism – Important MCQ

16. Which of the following is not a factor affecting the strength of Earth’s magnetic field?

(A) Geomagnetic reversals
(B) Earth’s rotation
(C) Distance from the magnetic poles
(D) Solar activity

(C) Distance from the magnetic poles
Explanation: Distance from the magnetic poles does not affect the strength of Earth’s magnetic field. The strength of the magnetic field is primarily influenced by factors such as the Earth’s core dynamics, the presence of molten iron in the outer core, and geophysical processes within the Earth.

17. The region of Earth’s magnetosphere where charged particles are trapped by the magnetic field is called the:

(A) Aurora borealis
(B) Van Allen radiation belts
(C) Polar vortex
(D) Coronal mass ejection

(B) Van Allen radiation belts
Explanation: The Van Allen radiation belts are regions of trapped charged particles (primarily electrons and protons) in the Earth’s magnetosphere. These belts are named after James Van Allen, who discovered them using data from the Explorer 1 satellite.

18. What is the term for the phenomenon where a magnetic field induces an electric current in a conductor?

(A) Electromagnetic radiation
(B) Magnetic resonance
(C) Faraday’s law of electromagnetic induction
(D) Ampere’s law

(C) Faraday’s law of electromagnetic induction
Explanation: Faraday’s law of electromagnetic induction states that a changing magnetic field induces an electric current in a nearby conductor. This phenomenon forms the basis of many electrical devices and technologies.

19. What is the average strength of Earth’s magnetic field at the surface?

(A) 1 tesla
(B) 10 milli Tesla
(C) 25 micro Tesla
(D) 50 nanotesla

(C) 25 micro Tesla
Explanation: The average strength of Earth’s magnetic field at the surface is approximately 25 micro Tesla (µT). However, it can vary in different locations and over time.

20. The study of the behaviour and effects of magnetic fields in the Earth’s upper atmosphere is known as:

(A) Aeromagnetism
(B) Magnetostriction
(C) Ionospheric physics
(D) Magnetic hysteresis

(C) Ionospheric physics
Explanation: Ionospheric physics is the study of the behaviour and effects of magnetic fields in the Earth’s upper atmosphere, specifically the ionosphere. The ionosphere is a region of the Earth’s atmosphere where the gas particles are ionized by solar radiation.

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Geomagnetism – Important MCQ

16. Which of the following is not a factor affecting the strength of Earth’s magnetic field?

17. The region of Earth’s magnetosphere where charged particles are trapped by the magnetic field is called the:

18. What is the term for the phenomenon where a magnetic field induces an electric current in a conductor?

19. What is the average strength of Earth’s magnetic field at the surface?

20. The study of the behaviour and effects of magnetic fields in the Earth’s upper atmosphere is known as:

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