A) can never reach the poles
B) can never reach the equator
C) require less kinetic energy to reach the equator than the poles
D) require greater kinetic energy to reach the equator, than the poles
Correct Answer: D
Solution :
Earths magnetic field at poles is vertical (perpendicular to earths surface) and horizontal (parallel to earths surface from south to north) at equator. Cosmic rays are positively charged particles, hence no magnetic force acts on cosmic ray particles coming at poles. Force \[=qvB\sin \theta \] At poles angle between \[\overrightarrow{\mathbf{v}}\] and \[\overrightarrow{\mathbf{B}}\], \[\theta =0\]; so, force on charged particle is zero. At equator \[\theta ={{90}^{o}}\] , so, force \[=qvB\,\sin {{90}^{o}}=qvB\] This force is maximum and deflects the particles sideways. Hence, only high energy particles can reach the equator.
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