# Find the Value of an Unknown Resistor.

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Introduction

To Find the Value of an Unknown Resistor

I will be making an experiment to find out the resistance of a piece of nichrome wire using.

I will be using Ohm’s law, which states that the current through a resistor is proportional to the voltage across the resistor providing that the temperature remains constant. Therefore, I will use the equation.

Resistance= voltage

current

There are three things that affect the resistance of a resistor.

- Increasing the length will give the current further to travel, which will increase resistance.
- Increasing the cross-sectional area of the material will give the current more space to flow through and so reduce the resistance.
- The material of the resistor also affects the resistance, because some materials are better conductors than others.

I will carry out my experiment three times to give a more accurate final reading. I will also keep the temperature constant so that it doesn’t have a big influence on the results of the experiment.

I predict

Middle

The process will be repeated two more times so that I will have three voltage readings for each specified current. I will add each set of three voltages together, and then divide by 3 to arrive at an average voltage reading for each point of current.

I will store the readings I have taken in a table and then plot voltage and current on the graph.

I expect to see on the graph I make a close fit straight line going through where current and voltage are zero.

## Experiment

The results of my experiment set out in a table.

Temp. of water (C) | Amps (I) | Volts (V) | Volts (V) | Volts (V) |

25 25 25 25 25 25 25 25 | 0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 | 1.72 2.89 3.95 5.14 6.34 7.41 8.36 9.71 | 1.69 2.89 4.03 5.22 6.32 7.25 8.42 9.745 | 1.74 2.93 4.03 5.02 6.37 7.40 8.55 9.71 |

Conclusion

The 3 tests of the same experiment on different currents read a similar voltage this shows that the results are quite accurate but not exact which may influence the average voltage to be different enough to make the plotted graph not to be accurate.

## Evaluation

I followed out the experiment as well as I could but certain things I believe would improve the experiment in future, they would be:

- Take my results quicker so the points would be more accurate as the graph on higher current readings started to curve upwards. This is because the higher the current the quicker the temperature of the water heats up, and as the water was contained in a beaker the water heated up faster.
- To help keep the temperature of the water constant, I would find a way to put the unknown resistor in flowing water so that the heated water around the resistor may flow away to keep the temperature of the unknown resistor more constant.

Extreme anomalous points were not found although there are points that don’t go exactly on the line on graph I have drawn.

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

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