A beam contains `2 xx 10^(8)` doubly charged positive ions per cubic centimeter, all of which are moving with a speed of `10^(5) m//s` . The current density is

Options

A. `6.4 A//m^(2)`
B. `3.2 A//m^(2)`
C. `1.6 A//m^(2)`
D. None of these

Answer

A

Explanation

`I = n(ze)Av_(d)`
`rArr I/A =J (ze)v_(d)`
`J = 2 xx 10^(8) xx 2 xx 1.6 xx 10^(-19) xx 10^(5)`
`= 6.4 xx 10^(-6) A//m^(2)`