Resistance of a Temperature, Lab Report Example

How does the resistance of a temperature dependent resistor depend on its temperature?

Design

Resistors have many practical uses in circuits. They can be used to produce heat, give off light, to control the amount of power that enters an electrical device, and to set voltages. As a consequence, it’s important to understand how temperature dependent resistors function. By determining how the resistance of temperature dependent resistors depend on its temperature, we can gain information that will allow us to optimize circuits, which may have a practical application for many household electrical products.

Variables

The independent variable in this experiment is temperature, measured in degrees Celsius. The dependent variable is the resistance, measured in kiloohms. The controls in this experiment include the equipment I used, including the ohmmeter, hot plate, and the thermometer, in addition to the volume of water in the beaker and the type of circuit set up for the experiment (series circuit). The equipment used in this experiment include an electric hot plate, a 600 mL beaker, a clamp holder and stand, a mercury thermometer, an ohmmeter, and electrical wires. A diagram of the setup is shown in figure 1.

Figure 1 Diagram of the experimental setup

Experimental Method

As shown in figure 1, two wires are set up in a series circuit. They are also connected to an ohmmeter so the resistance of the process can be measured. A wire from the circuit is placed into a beaker of water on a hot plate so the temperature of the system can be manipulated. A thermometer is placed in the beaker to ensure that temperature manipulations are accurate. To ensure the controls are kept fixed, the volume of water in the beaker is constantly monitored and filled back to constant volume if water is spilled or evaporates. In addition, the materials used are kept constant throughout the experiment. To measure the first data point, the temperature of the hotplate will be adjusted to 30 degrees Celsius. To ensure the system is this temperature as well, the temperature of the thermometer in the beaker will be examined. When the temperature set on the hotplate matches the temperature read on the thermometer, the measurement on the ohmmeter will be recorded. This process will be repeated using temperature measurements in increments of 10 degrees Celsius until the maximum of 80 degrees Celsius is reached.

Data Collection and Processing

The experiment was repeated three times. This data is compiled below in table 1. While the ohmmeter measurements can be considered accurate, we should consider an uncertainty of plus or minus .001 kiloohms. This is reasonable because the ohmmeter only displays values with three decimal places on the screen, and we cannot be certain of the number in the fourth decimal place, which may affect the rounding of the numbers that are displayed. Table 1 shows the measurements as they were read on the ohmmeter and all calculations were performed with the assumption that the ohmmeter reading was accurate.

Table 1 The relationship between increase in temperature of the circuit and resistance.

Processing Raw Data A

A summary of the data collected in the experiment is shown in table 2.

Table 2 The average, maximum, and minimum resistance according to temperature and the associated random error.

Table 2 shows that the maximum random error is 0.003 for this data set. As a consequence, the collected data could be considered precise. All calculations were performed using Microsoft Excel functions. The maximum random error was 0.003. This demonstrates that kiloohm measurements were precise in this experiment and it is unlikely that values were received as a result of chance.

Presenting Processed Data

Figure 1 below shows a scatterplot that compares the relationship of temperature change to resistance in kiloohms.

Figure 1 Relationship between temperature increase and resistance

Conclusion

Figure 1 demonstrates that as temperature increases, resistance of a circuit also increases. On first inspection, it appears that this relationship is proportional. The lines of max-min gradient do not contain the origin, because in this particular experimental setup, it is not possible for there to be a negative temperature. In addition, even when the temperature is 0 degrees Celsius in this setup, we would expect some resistance in the system. While the relationship between temperature and resistance appears to be proportional, the mathematical equation in figure 1 confirms this. It should also be noted that the correlation constant is 0.99, which confirms this. These results make sense in light of Ohm’s law, which states that the current of a circuit is equal to the potential difference measured across the conductor in volts, divided by the resistance of the conductor in ohms. It is important to note that the potential difference measured across the conductor in volts is dependent on a variety of factors. One of these is the material that is being used as the conductor, and others, such as temperature, are able to influence the state of the conductor. As a result, the temperature has an impact on the conductivity of the circuit system, which is reflected when resistance is measured (Shedd et al., 1913).

Evaluating Procedures

The line does not pass through the origin due to the nature of the experimental setup. There will always be resistance in the system, even if the temperature is 0, due to the nature of the circuit. Therefore, unless the temperature is negative, there will not be a lack of resistance in this system. It may be possible to manipulate the experiment so this is the case, but this is not within the scope of this specific experimental design. It is unlikely that random error and reading error were a serious concern to the efficacy of the results in this project. All of the results were precise for each temperature data point and the maximum random error received was 0.003, which can be considered to not have a significant impact on the results after uncertainty is considered. Fortunately, the data analysis demonstrates that there were no significant errors made throughout this project. In addition, there were no noticeable errors during the data collection portion of this experiment.

Improving the Investigation

To be sure that the resistance of the circuit increases as temperature increases, it would be useful to repeat this experiment using negative temperatures. Since temperatures between 30 and 80 degrees Celsius were used in this experimental setup, the follow up experiment should use -30 to -80 degrees. If the relationship between temperature and resistance is proportional, we would expect a graph similar to the one plotted in figure 1. This evaluation would also help us understand the extent to which the system may stop working due to too low temperatures. This would provide us an important real world application about the circuits we use in our own homes. At what temperature will our circuits stop working? With this knowledge, we could direct suggestions to homeowners about what they can do to protect their circuits in cold weather. This may be useful for people who live in colder climates, such as Russia.

References

Shedd J, Hershey MD. (1913). The History of Ohm’s Law. Popular Science. Bonnier Corporation.