# Current density, resistance and resistivity problem

1. Oct 21, 2008

### ctpengage

In a problem it states that:

A 10.71 V battery is connected to a resistive strip that consists of three sections with the same cross-sectional areas but different conductivities.

In the solution to the problem it stipulates that the current density of the three sections are equal. Where in the above statement does it imply that.

2. Oct 21, 2008

### ctpengage

3. Oct 21, 2008

### Rake-MC

Think about what the definition of current density is. Also, is current conserved?

4. Oct 12, 2010

### subxaero33

charge and current are reserved.

I am also working on this problem, but when I calculate the current density from the third section (since I am given the third section's conductivity) I am getting the wrong answer for the conductivities of parts 1 and 2..

charge density = conductivity of part 3 * electric field of part 3

J = $$\sigma$$ * E3

The current of the battery flows through the 3 part resistive strip to the negative terminal of the battery.

the distance on the strip is defined as 0 at the positive connection side of the strip and 9.12mm at the negative side of the strip.

I then use the equation

conductivity = J / E per part

to calculate conductivity of parts 1 and 2.

Im getting this wrong so Im guessing calculating J is wrong. Can someone steer me in the right direction?

5. Oct 12, 2010

### subxaero33

I figured it out!

I was reading the graph values wrong in that it was x10^3 and not x10-3