Current and electric field strength question

[downwithsocks]

Homework Statement

A wire carries a current and consists of three sections with different radii. Rank the sections according to the following quantities, greatest first: (a) current, (b) magnitude of current density, and (c) magnitude of electric field.

Homework Equations

i = int(J).dA

The Attempt at a Solution

a) A = B = C since charge is conserved and the same amount of current must enter and leave each section. Is this correct?

b) From the given equation, J = i/A. So the cross section with the greatest area will have the lowest current density, thus B > C > A. Correct?

c) Intuition tells me A > C > B but I can't even really convince myself that that's correct let alone explain why with an equation, could anybody help me along?

 

[SammyS]

Which section has the greatest voltage drop? Then use: E=-ΔV/Δx .

 

[downwithsocks]

I'm not sure how to tell which section has the greatest voltage drop...looking in my book I can't find an equation that relates voltage and area..

 

[SammyS]

Resistance ? Resistivity ? Ohm's Law ?

 

[downwithsocks]

V = IR? Wouldn't I need a value for the resistivity then?

 

[gneill]

I'm not sure how to tell which section has the greatest voltage drop...looking in my book I can't find an equation that relates voltage and area..

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/resis.html"