Moving Charges n Uniform Magnetic Field?Change n Kinetic Energy181 Moving charge

Question

Moving Charges n Uniform Magnetic Field?Change n Kinetic Energy181 Moving charged particles are released with a velocity (details listed below) at the point P (2 m, 2 ,m) in a large region of space that has a uniform magnetic field in the +x direction. All these particles have the same mass, and they are released individually into this field. Rank from greatest to least the change in kinetic energy of these charged particles after they have traveled 1 cm from P. Or, the change in kinetic energy will be the same for all of these (but not zero). ___ Or, the change in kinetic energy will be zero for all of these. _____________ Please carefully explain your reasoning.

Explanation / Answer

By work energy theorem,

W = delta(KE)

However, the magnetic field does not do work at all, because it only functions when v is perpendicular to B. In which case, it exerts a force perpendicular to v, hence to the displacement.

Thus,

W = delta KE = 0   [The change in kinetic energy will be zero for all these.]

as a magnetic field is the only force here.

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