Electricity and Magnetism · Problem 4.20

THE FIELDS OF MOVING CHARGES — Edward Purcell & David Morin

Physics — E&M · combining-the-current-densities

Problem

Combining the current densities ** We have

5 \cdot 10^{16}

doubly charged positive ions per m

^3

, all moving west with a speed of

10^5

m/s. In the same region there are

10^{17}

electrons per m

^3

moving northeast with a speed of

10^6

m/s. (Don't ask how we managed it!) What are the magnitude and direction of

\mathbf{J}