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The aim of this experiment is to investigate the relationship between the current, voltage and resistance through the use of a fixed resistor and a filament lamp.

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Abdul Mufti                                               Centre Number: 13329                                 Candidate Number: 4138  

10. F


The aim of this experiment is to investigate the relationship between the current, voltage and resistance through the use of a fixed resistor and a filament lamp.


Based on knowledge of Ohm’s law it can be hypothesised that when an increasing voltage and current is passed through a filament lamp the resistance would increase in an irregular fashion, so that a graph similar to the one given below would be seen (figure 1). This curved graph would be expected due to temperature increases in the filament lamp.

It can also be hypothesised that when current is passed through a fixed resistor  a straight line graph would be obtained (figure 2) this  is explained in figure 3.




Circuit Diagrams





Fixed resistor &

Filament Lamp         to impede and obstruct current flowing through circuit

Ammeter                 to measure current flowing through the circuit

Voltmeter–         to measure the voltage present in the circuit and to make sure the power supply is correctly calibrated.

Power Supply–         to act as the adjustable power source for the circuit

Wiresto connect the circuit components. Tangles were removed from the wires as not doing so could result in erroneous values being obtained in the experiment, as using several different wires or tangled wires during the experiment could lead to varied resistance and poor fair test (Figure 6).


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The equipment was then turned on. As the voltage on the PSU was increased it was confirmed on the voltmeter and the reading on the ammeter was noted. For the first circuit a total of 7 ammeter readings were taken and repeated. Each time the voltage was increased by 2 V.

The value for each voltage was recorded in the table. Once the highest voltage had been reached for the PSU the circuit was switched off and the fixed resistor was replaced with a filament lamp (figure 6). The voltage readings were then repeated as before and were inserted in another table. After this the equipment was cleared away. The tables were then plotted onto graphs.

Method in summary:

  1. Apply safety precautions.
  2. Gather equipment and connect it according to figure 4.
  3. Recheck for safety and turn the circuit on.
  4. Increase the Voltage by 2V every reading and note the current reading on the ammeter.
  5. Once 12V is reached switch the PSU off.
  6. Replace resistor with a Filament Lamp
  7. Carry out steps 3-5 again.
  8. Once readings for filament lamp and fixed resistor are tabulated clear up equipment.
  9. Plot an I-V graph for the fixed resistor and Filament Lamp.


The controlled variables in this experiment are the resistors and equipment used.

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To conduct a fair test it would have been practical to use averages for a series of current readings. This could be done by using two different sets of equipment, conducting the experiment on each set and averaging the values. This could help us reduce the margin of error in any anomalies found. It may have been interesting to investigate the same aim with a wider range and more sensitive set of equipment. Smaller increases of voltage on the PSU would have allowed us to plot the graphs with more accuracy. If possible it would have been interesting to use a diode. We may also have adjusted variables such as the thickness, length and type of wire used to investigate the effect these factors have on Ohm’s law and our graphs. we would also investigate how changing the circuit diagram would have affected our results.

However it would not have been possible because of time limitations


GCSE double Science Physics – CGP – ISBN: 1-84146-401-5

New Modular Science for GCSE, (Vol 1), - Heinemann (1996) – ISBN: 0-43557-196-6

AQA GCSE Science syllabus (2001).

A level Physics Letts Study Guide (reprinted 1996)

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