Experiment - Ohm's Law and Power

In this experiment you will explore Ohm's law and use graphical analysis to determine the resistance of a fixed resistor.  Ohm’s Law says resistance = volts/current. This relationship can be determined by measuring the voltage and current operating through an electrical component. 

All appliances that do work such as operate an electric motor or heat or give out light are resistors. All resistors transform electrical energy into some other form of energy.



To explore Ohm's law and use data collected on the current flowing through a fixed resistor as the applied voltage is changed to determine the resistance of a particular metallic resistor.  

Apparatus (Equipment)

1 x fixed resistor (between 5 and 10 ohms)

1 x 0 to 12V voltmeter

1 x 0 to 5A voltmeter

1 x Variable DC power supply (2 to 12V)

5 x conducting wires with suitable attachments.(Do not use long wires) 


Using the equipment, carefully construct the following circuit. Do not turn on the power yet.

The switch on the power pack should only be switched on for very short periods while readings of the meters are made. Leaving the power on too long may change the temperature of the wires too much and spoil your results.

The power pack was set to the lowest setting (~2V).

The switch was closed momentarily to check that the needle of both meters deflected in the right direction.

A table to record results was prepared with two columns, one to record the ammeter readings and the other the voltmeter readings.

The switch was again closed and the readings on the ammeter and voltmeter for the lowest power setting were noted and recorded in the table.

This was repeated for each successively higher setting from the variable power supply until the maximum setting was reached (12V). The results were readings on the ammeter and voltmeter were recorded in the table for each available setting from the power supply.

Important: The power was only switched on briefly to allow the readings of the meters to be taken and then the resistor was allowed to cool between each measurement.
A graph of "The current read on the ammeter" versus "the voltage read on the voltmeter". The current was plotted on the 'y' axis while the voltage was plotted on the 'x' axis.
Based on theory, the slope of the line for the graph drawn is equal to the resistance of the fixed resistor in the circuit. The value was determined and a conclusion to the experiment was written. 


  1. What were the independent and dependent variable in your experiment?
  2. Name a control that you applied during the experiment.
  3. Can you explain why the slope of the line on the graph you drew represents the resistance of the fixed resistor in the circuit?
  4. Describe how the results you collected could be made more reliable? Consult your teacher if you are not sure.
Electrical cord