Resistance of human body
========================

We have seen that an unknown resistance can be measured by comparing with a known resistance
by connecting them in series and measuring the voltages across them. This technique can be used to
measure the resistance of human body.

Objective
---------
Measure the resistance of human body by comparing it with a known
resistor, for DC and AC voltages.

.. image:: schematics/res-body.svg
   :width: 300px

Procedure
---------

-  Set PVS to 3 volts
-  Connect a wire from PV1 to A1
-  Connect one end of a wire to PV1
-  Connect one end of another wire to A2
-  Connect a :math:`100\Omega` resistor from A2 to ground.
-  Enable the Checkboxes to display A1 and A2
-  Hold the unconnected ends of both wires by your hands.
-  Repeat using SINE instead of PV1. 
-  Enable amplitude and frequency display for A1 and A2.

.. image:: pics/res-human-screen.png
	   :width: 400px
	   
Discussion
----------
The AC resistance is less than the DC resistance. The resistance is due
to our skin and AC can pass through this, like it passes through the
dielectric material of a capacitor. A bit of exploring will reveal that
a capacitor is formed between the tip of the wire and blood inside
with the skin acting as a dielectric. Explore the effect of a metal plate
at the tip of the wire.
