Speaker A
Lesson three. Laboratory work number one. Investigating the dependence of a metal conductor's electrical resistance on temperature. 3D version. The goal of the work is to experimentally confirm that the electrical resistance of metals increases with temperature. To show that the dependence of a metal conductor's resistance on temperature is nearly linear. To determine the temperature coefficient of metal resistance; equipment: personal computer or smartphone and an interactive 3D simulator. In this lab work, we will investigate how the resistance of a metal conductor changes with temperature. Usually, a special device is used for this, which allows studying the dependence of metal resistance on temperature. During the experiment, a setup is assembled in which a metal wire is heated using hot water in a container. As heating progresses, the wire temperature gradually increases, and its resistance is simultaneously measured with a multimeter. The results obtained will allow us to experimentally verify that the resistance of a metal conductor depends linearly on its temperature. However, if it is not possible to assemble the recommended experimental setup, the lab work can be performed using an interactive 3D simulator, available on a PC, tablet, or smartphone via the link easily found in the description of this video. This application was developed in accordance with the requirements of this laboratory work. So, first, open the interactive application using the link in the video description. Second, if necessary, you can change the copper conductor to another one. Third, turn on the heater, the start button. Record the wire resistance every 5 °C in the range from 25 °C. Enter the corresponding data into the table shown on the screen. But before you start the experiment, you should watch the video to the end and take into account the following tips when using the simulator. The virtual simulator consists of two main parts. On the left is the simulator control panel, and directly in the middle or slightly to the right is our virtual experimental setup, with which we will investigate the dependence of a metal conductor's electrical resistance on temperature. On the stand, there is a device for measuring temperature in degrees Celsius, which is connected to the heater. The heater heats the metal conductor, which is in this original form. To make our virtual simulation look more interesting, it is placed on this heating plate and connected in series to an ohmmeter for measuring resistance. The ohmmeter display shows the resistance value of the given metal conductor. Specifically, at a room temperature of 20 °C, it equals 4.24 ohms. And the conductor material is copper. We can also select several other materials from the list, such as aluminum, silver, or gold. We will experiment with a copper conductor, which needs to be heated from a temperature of 20 °C or, if necessary, even up to 100 °C. The simulation speed can be changed, but it is recommended to perform the experiment in real-time, when the resistance and temperature of our metal conductor change as slowly as they would in a live, real-world experiment. To start the process, as we can see, of increasing the temperature, that is, heating, we press start. When heating is underway, the temperatures begin to rise. And, as we can see, the resistance also changes. At 5 °C increments, we must record this data and enter it into the table. In the background, on a special interactive board, a graph of resistance versus temperature is plotted in real time. We will build something similar, but with much less data. So, 25.31 ohms. At 25 °C the conductor resistance value was equal to 4.31 ohms. This data must be entered into the table. To change the camera position, use the mouse. Hold down the right button to move our scene around. Hold down the left button to rotate it. The scroll wheel allows you to zoom in or out. 30 °C 4.4 ohms. We enter this data into the table. Furthermore, every time we open the simulator or refresh the page, we get a metal conductor with different resistance. We can choose the conductor material, but the resistance constantly changes, so be careful during the experiment—35 ° 4.5 ohms—during the experiment and do not refresh the page unnecessarily. Today we will have a creative task, so we will need this specific conductor with this resistance later. In order to stop the heating process, there is no special button provided. In real life, when we conduct such an experiment, we cannot stop the measurement process, step away for half an hour, and then return to continue. We would definitely have to start everything over from the beginning. Likewise here, the most we can do is reset and begin plotting and taking the corresponding experimental results from the initial temperature set on the control panel. We will not record all the data, but during the experiment, according to the requirements already stated, it is necessary to take resistance readings versus temperature in the range from 20 to 80 °C at 5 °C increments. Fourth, plot the graph of the wire's resistance dependence on its temperature according to the table data, as shown in the figure. To do this, first plot all the points you recorded, then draw a straight line that best fits them. We will plot a fragment of the graph based on the data taken from our virtual simulator. The first thing to do is to choose an optimal and suitable scale for both the temperature axis and the resistance axis. For this, let's recall that the temperature changes in a range from effectively 0 to 80 °C. The most convenient option would be if we choose a scale of 10 °C for every two grid squares. Then, one more square, the next, will correspond to the 15, 25, 35, 45, and so on-degree marks. For resistance, we will choose the scale based on the data we have recorded. So, at 25 ° we have 4.3, if we round it to ohms, and at 45, 4.68 or 4.7 ohms. Thus, the step we will take, which is the most optimal, looks like this: four 4.1, 424, 467 for the data we have. This is quite enough. After that, we start plotting the points. For 25 °C, the value is 4.31. In other words, right here is where our point corresponding to the collected data will be located. At 30 °, the resistance value is 4.4 ohms. At 35, 4.5 ohms; so far everything is going too smoothly. But at 40, we have a fluctuation of 4.56, and at 45, 4.68. Thus, by constructing the curve through the points, we get that at 0 degrees, the resistance value of our conductor will be equal to approximately 3.8–3.9 ohms. This line will be drawn more accurately the more data you have. There is no point in adding points to the graph that correspond to higher temperatures, because everyone using the simulator will get different experimental data for their own graph. Fifth, determine the temperature coefficient of resistance of the metal. To do this, first extend the graph of resistance versus temperature to the intersection with the ordinate axis and determine the resistance R₀ at 0 °C. Select any point on the graph and take the resistance value R and temperature T. And record this data. Calculate the average value of the temperature coefficient of resistance, alpha average of copper. For this, it is necessary to divide R minus R₀ by R₀ times T. You performed the values of R₀, as well as the chosen value of R and T, in the previous step. Compare the obtained value of alpha average with the table value of the temperature coefficient of resistance of copper, which is equal to 0.041 per degree. Formulate a conclusion in which you state, first, what exactly you investigated during the laboratory work. Second, how did the resistance of the metal conductor change with increasing temperature in your experiment? Third, how linear is the dependence of the wire's resistance on temperature according to the graph you plotted? And fourth, what is the obtained value of alpha average and what is the reason for the measurement?
