# How to Calculate Current Density (Petri Dish/Graphite 0.7 mm)

1. Jul 27, 2017

### TGH904

Hello all,

I have a petri dish 8.7 cm in diameter filled with 20 mL of TSB media. I have set up a .7mm graphite at the 0cm mark of the diamter and measured current at 4.6Volts over the entire distance of the petri dish (8.7cm) with .5 cm step sizes. For example:

When the probes are 1cm apart I am reading a current of 2.8mA.

I was wondering how I can calculate a current density for all the known information.

Current Density (J) = Current (I) / Area (A)

How could I calculate the area if I am 1 cm apart in a 8.7 cm petri dish?

2. Jul 28, 2017

### Fernando Perfumo

Hello. You can estimate resistivity by filling a long and thin tube with that liquid and calculate its resistance. It adds some more info relating to the voltage too.

3. Jul 28, 2017

### TGH904

What I want to understand about current density when measuring do I treat the path of current in a liquid as a linear region in 2D, or as a gradient in 3D