Leaf Tissue Resistivity! (very confused please help me)

Question

Resistivity measurements on the leaves of corn plants are a good way to assess stress and overall health. The leaf of a corn plant has a resistance of 1.9 MΩ measured between two electrodes placed 20 cm apart along the leaf. The leaf has a width of 2.9 cm and is 0.20 mm thick.

What is the resistivity of the leaf tissue?

Answer 1

Corn leaves are very long and narrow.

This exercise concerns calculating resistivity along its length from measurements of resistance.

Resistivity determines resistance -- the longer the distance along the leaf the larger the resistance, and

the bigger the cross section the smaller the resistance.

The relationship is expressed by

R = ρL/A

where

ρ is resistivity,

L is the distance between electrodes,

A is the cross section of the leaf,

R is the resistance.

Given R and the other quantities you can calculate

ρ = RA/L

For your data

R = 1.9Ω

L = 20cm

A = 2.9cm × 0.20 mm = 0.058 cm²

So

ρ = 1.9Ω × 0.058 cm² / 20cm = 0.00551 Ωcm = 0.0000551 Ωm