Investigation activity. Video (1 min) with exercises
This time, you will be the scientist who investigates which variables influence resistance. In the following video, your assistant will make some changes in a cable to see what effect they have on resistance. As a good scientist, he/she will change only one characteristic of the cable at a time, leaving the others constant.
There are three characteristics of the wire that you could change. One is the type of material it is made of. The quantity we use to indicate how difficult it is for electric current to flow through a certain type of material is resistivity, which is symbolized by the Greek letter ρ (read "rho").
What other two cable characteristics do you think you could change? Think about it before you hit play. You'll find the answer in the video.
After watching it, answer the questions.
Self-created video based on PhET Interactive Simulations , University of Colorado Boulder, https://phet.colorado.edu, CC-BY-4.0
What happens if you increase the length of the wire? The resistance increases because the electrons have to travel a greater distance, and therefore they will lose more energy colliding with the atoms that make up the wire on their way. We say that resistance and length are directly proportional magnitudes, since when one increases, the other increases proportionally.
What happens if you increase the area or section of the wire? The resistance decreases because the electrons have a larger gap to pass through, and they will find less opposition to pass through there. Area and resistance are inversely proportional magnitudes, because when one increases, the other decreases proportionally.
What happens if the wire material has a higher resistivity? The resistance increases. Resistivity and resistance are directly proportional.
After having analyzed the results that your assistant has provided you, it is time to draw conclusions and write them down in the universal language of mathematics. Do you dare to propose a formula?: R = ro ρ · times L / divided by A
