Suppose drift velocity over the entire cross section of a wire is V (r) = `V_(0) [ 1 - (r)/(R) ] `. What is the current density at the surface of the wire ?

Options

A. zero
B. `V_(0)`R
C. ne`V_(0)`
D. ne`(r)/(R)`

Answer

A

Explanation

zero
`V_(r) = V_(0) [ 1 - (r)/(R) ] ` on the surface , taking r = R.
`therefore V_((r)) = V_(0) [ 1- 1 ] `
`therefore V_((r)) = V_(0) [0] =0 `