A beam contains `2.0xx10^8` doubly charged positive ions per cubic centimeter, all of which are moving toward north with a speed of `1.0xx10^5 ms^(-1)`. (a) what are the magnitude and direction of the current density `vecJ`? (b) can you calculate the total current i in this ion beam? If not what additional informaiton in needed.

Explanation

a. `J =nqv_d = (2xx10^8xx10^(6))xx(2xx1.6xx10^(-19))xx10^(5)`
`=6.4 Am^(-2)`
As the velocity of positive ions is toward north, the direction
of `vecJ` will also be toward north.
b. No, we need area of cross section of the wire.