
Aim: to investigate the behaviour of Resistors and
to verify the formulae for calculating the Effective
Value of Resistors connected in Series and in Parallel 
See Resistance,
Finding the Equivalent Resistance of a Circuit 

Method 
Obtain results from which you could plot graphs of
voltage (horizontal) against current for (at least) two
resistors separately and then for the same two
resistors connected 
i) in series and 
ii) in parallel with each other. 
Plot the graphs and use them to calculate the
resistances, R_{1}, R_{2} and R_{e1}
(series) and R_{e2} (parallel). 

A graph of voltage across a component against
current flowing through the component is called the
characteristic of the component. 
To obtain the electrical characteristics of a
component we need a variable voltage supply. 
A simple way to produce a variable voltage supply
from a fixed voltage supply is by using a rheostat
(variable resistance) as a variable potential divider
as shown in the circuit diagram below. 

A variable potential divider circuit is useful in
this and many other similar experiments but it should be
noted that it is not a very stable voltage
source. 
To see this, try setting the sliding contact S to
give a voltage of 3V with the resistor, R, removed from
the circuit. 
Now connect the resistor back in the circuit. 
Notice that the reading of the voltmeter changes... 