# Resistivity - Limiting factors?

• cbs27
In summary, the speaker describes their experimental method for a coursework assignment, which involves measuring a resistive wire and using a voltmeter to measure the voltage. They also mention taking precautions to ensure accurate readings, such as using short wires and measuring the thickness of the wire. They then explain their process for obtaining data and calculating the resistivity of the wire. They end by thanking for any potential help.
cbs27
I have a piece of coursework due in soon (as a matter of fact, about 2 hours from now), and I need to know what the lmiting factors were. Here's the method:
(a copypasta from my handed-in plan)

For this experiment, I measured out a length of a resistive metal wire, and connected it to the circuit as shown above. I kept the wires that I used as short as possible, because even though they have very low resistance, they may affect my readings. Also, I connected the voltmeter as close as possible to the resistive wire in order to measure only the voltage across the resistive wire. I measured the thickness of the resistive wire using a micrometer; I took three readings at various points throughout the section of wire I used, and made an average in order to be more accurate, being careful not to squash it. I measured out 1m of the resistive wire using a metre rule, being careful to straighten out any kinks in the wire. I then attached it with crocodile clips to the circuit. I checked first of all to see if there was a 0 error on the ammeter or voltmeter, and then to see the lowest voltage at which I could get suitable readings in the interest of safety, and found I could obtain a result from 3v. I then passed this voltage through the resistive wire, and took-down readings from the ammeter and voltmeter; being careful to run the current for as little time as possible so that the temperature of the resistive wire did not increase a lot, disturbing my readings. I then switched it off and repeated the experiment from 100cm at 10cm intervals down to 10cm with 3 repeats for each length, and an average made of the three for increased reliability of data. I waited in between the tests long enought for the wire to cool down in order to minimise the change in temperature.
Using the data I could then work out the resistivity of the wire, using:
ρ = RA/L Where ρ = Resistivity
R = Resistance
A = Cross-sectional area of the wire
L = length of the wire

Regards,
cbs27

It would be helpful to connect the voltmeter directly to the resistance wire just inside the clips and the distance between the voltmeter connections becomes the length of wire to be considered.

Hello cbs27,

The limiting factors in your experiment are the resistance of the wires used, the accuracy of the measurement devices (voltmeter and ammeter), and the change in temperature of the resistive wire.

As you mentioned, the wires used to connect the circuit have a small amount of resistance which can affect your readings. To minimize this, you kept the wires as short as possible. However, in future experiments, you may want to consider using wires with even lower resistance to further minimize this factor.

The accuracy of your measurement devices is also a limiting factor. Even small errors in the readings can affect the final result. To improve the accuracy, you can calibrate your devices before the experiment and take multiple readings to calculate an average.

The change in temperature of the resistive wire can also affect the results of your experiment. As the wire heats up, its resistance may change, leading to inaccurate readings. To minimize this, you took care to run the current for as short a time as possible and waited for the wire to cool down before taking further measurements. However, in future experiments, you may want to consider using a wire with a higher melting point or using a temperature-controlled environment to keep the wire at a constant temperature.

Overall, by being aware of these limiting factors and taking steps to minimize their impact, you can improve the accuracy and reliability of your results. Good luck with your coursework!

## 1. What is resistivity?

Resistivity, also known as electrical resistivity, is the measure of a material's ability to resist the flow of electric current. It is represented by the Greek letter rho (ρ) and is measured in ohm-meters (Ω•m).

## 2. What are the factors that affect resistivity?

There are several factors that can affect resistivity. These include the type of material, temperature, length and cross-sectional area of the material, and impurities or defects in the material.

## 3. How does temperature affect resistivity?

In most materials, an increase in temperature leads to an increase in resistivity. This is because as the temperature rises, the atoms in the material vibrate more, causing more collisions with the electrons and hindering their movement, thus increasing resistance.

## 4. How do impurities affect resistivity?

Impurities in a material can disrupt the regular arrangement of atoms, creating more obstacles for the electrons to pass through. This leads to an increase in resistivity and decreases the material's conductivity.

## 5. What is the relationship between resistivity and conductivity?

Resistivity and conductivity are inversely related. As resistivity increases, conductivity decreases, and vice versa. This means that materials with high resistivity have low conductivity, and materials with low resistivity have high conductivity.

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