
Aim: to measure the Internal Resistance of a
Battery 
The final result will be taken from a graph
showing the electrical characteristics of the battery. 
See Observing the effects of the internal
resistance of a battery, The Internal
Resistance of a battery 

Method 
In the following circuit a bulb is included simply
to limit the maximum current. 

The internal resistance of a battery is not constant
but increases as the battery is used. 
For this reason do not leave the circuit connected
longer than is necessary to take the readings. 
It's also probably easiest to measure the internal
resistance of a new battery (or a recently charged
battery if you are investigating rechargeable
batteries). 

Most electrical characteristics
are plotted with V horizontal and
I vertical. 
This ia based on the logic that the potential
difference causes the current to flow (so potential
difference independent variable and current
dependent variable). 
However, it is reasonable to suggest that the
terminal potential difference of the battery depends on
the current we take from it thus we usually plot battery
characteristics with I horizontal
and V vertical. 
The equation relating I and
V is 

This is the equation of a straight line of slope r
so we expect a graph looking something like this: 
