Question

I need a proper solution for this question ( well explained and understandable writing)

Charged particles from outer space, called cosmic rays, strike the Earth more frequently near the poles than near the equator. Why?

Answer 1

The magnetic field of the earth resembles that of a giant bar magnet buried deep inside the earth. The north pole of this imaginary bar magnet is located near the geographic south and the south pole is located near the geographic north. Thus the magnetic flux lines emerge vertically up from the ground near the geographic south. Then the flux lines start tilting towards the horizontal as we walk north along the surface of the earth. The lines become parallel to the ground near the equator. Then they start dipping towards the ground as we move into the northern hemisphere. Finally, they point straight into the ground at the north pole.

The cosmic rays are nothing but high energy protons. They strike the upper atmosphere, interact with the matter, and trigger the generation of more exotic particles. Suppose these charged particles move down towards the earth. Then near the north pole their velocity vector is parallel to the magnetic field of the earth. Hence they experience no force. So they proceed straight ahead and reach the lower atmosphere. A similar thing happens at the south pole since the angle between the velocity and the field direction is 180 degrees. Then again the cross product of magnetic force vanishes.

However, near the equator, the velocity vector is perpendicular to the field direction. Therefore the Lorentz force is maximal and it deflects the positively charged incoming particles to the east and the negatively charged particles to the west. So they are no longer able to penetrate into the lower atmosphere.