Based on Ohm’s law materials are classified into two categories. Those
which obey Ohm’s law are called ohmic materials. For example, metals
are ohmic materials. Those which do not obey Ohm’s law are called non
ohmic materials. For example, LEDs are non ohmic materials.

Ohm’s law is valid for metal conductors provided the temperature and
other physical conditions remain constant. The resistance of the material
changes with temperature. Hence for changing temperature the V-I graph
for a conductor will be non-linear. Ohm’s law is not applicable to gaseous
conductors. It is also not applicable to semiconductors such as germanium
and silicon.

When a conductor is connected to a battery the free electrons start
moving with a drift speed in a specified direction. During the motion, the
electrons collide with positive ions (fixed) of the lattice and come to halt.
This means that they lose mechanical energy in the form of heat. Due to
the electric field that was set up by the battery throughout the conductor,
these electrons regain the energy from the field and proceed to move. The
motion of electrons is obstructed by the lattice ions. The obstruction
offered to the flow of electrons in a conductor by lattice ions depends
upon the nature of the material.

Therefore, the resistance of a conductor is defined as the obstruction
to the motion of the electrons in a conductor. The material which offers
resistance to the motion of electrons is called resistor.

Let us assume that human body is a resistor. The resistance of the
human body generally varies from 100 Ω (if body is wet with salt water)
to 5,00,000 Ω (if the skin is very dry). Let us calculate the amount of
current that flows through the human body. Let us assume you have touched
the two electrodes of a battery of 24V with dry fingers in such a way that
the circuit is complete. Let your body resistance be 1,00,000Ω. Then the