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NEET PHYSICSMAGNETISM AND MATTEREasy

Question

A compass needle which is allowed to move in a horizontal plane is taken to a geomagnetic pole. It:

A

will become rigid showing no movement

B

will stay in any position

C

will stay in north-south direction only

D

will stay in east-west direction only

Step-by-Step Solution

  1. Earth's Magnetic Field at Poles: At the geomagnetic poles, the magnetic field lines of the Earth are directed vertically (perpendicular to the surface). This means the angle of dip (or inclination, II or δ\delta) is 90∘90^\circ .
  2. Horizontal Component: The horizontal component of the Earth's magnetic field (HEH_E) is related to the total magnetic field (BB) and the angle of dip by the equation: HE=Bcos⁡δH_E = B \cos \delta At the poles, since δ=90∘\delta = 90^\circ, HE=Bcos⁡90∘=0H_E = B \cos 90^\circ = 0. Thus, the horizontal component of the Earth's magnetic field is zero.
  3. Effect on Compass: A compass needle is designed to move in a horizontal plane and aligns itself with the horizontal component of the magnetic field. The torque (τ\tau) exerted on the needle is given by τ=mHEsin⁡θ\tau = m H_E \sin \theta. Since HE=0H_E = 0, the torque is zero regardless of the orientation (θ\theta) of the needle.
  4. Conclusion: With no restoring torque to align it to a specific direction, the compass needle is in neutral equilibrium and will remain in any position in which it is placed.

Exam Context & Concepts Covered

This question aligns with the NEET PHYSICS syllabus, specifically targeting concepts from MAGNETISM AND MATTER. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

PHYSICSMAGNETISM AND MATTERcompassneedleallowedhorizontalgeomagnetic

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