Question

Most of the resistance of the human body comes from the skin, as the interior of the body contains aqueous solutions that are good electrical conductors. For dry skin, the resistance between a person's hands is measured at typically 500 kΩ. The skin varies in thickness, but on the average it is about 2.0 mm thick. We can model the body between the hands as a cylinder 1.6 m long and 14 cmin diameter with the skin wrapped around it.

(a) What is the resistivity of the skin?
Ω · m

(b) Compare your answer with the internal resistivity of the body, approximately

4.8 Ω · m.

rhoskin
rhointerior
=

How do you explain the fact that the resistance of the skin is about 1000 times greater than the internal resistance of the body, even though the resistivity of the skin is only about 60 times that of the interior of the body?

A )The skin has a smaller cross sectional area.

B )The resistance of an object scales exponentially with respect to the resistivity of the material out of which it is made.

C ) The skin is constantly moistened by biological processes.

D ) Charges can only exist on the surface of conductors.

Answer 1

a) Resistivity=R.A/L

Here, R=500000ohm, L=1.6m, A=2pi* (0.14/2)*0.002 m2=0.00088.........we have converted quantities into SI units

Resistivity=R.A/L

=500000*0.00088/1.6 = 440/1.6= 275 ohm.meter

b) pskin/pinterior =275/4.8=57.3

For second part, correct option is (A), because cross section area is smaller.