1. High Voltage Power Transmission for AP Physics
Betsy Hondorf, Oak Ridge High School, Oak Ridge, TN
INVESTIGATING LINE LOSS IN HIGH VOLTAGE POWER TRANSMISSION
A lesson, lab activity and research assignment to instruct and engage AP Physics students with high voltage power transmission
OBJECTIVES
AP Physics C- Electricity and Magnetism, Grades 11-12
Students will participate in a lesson on electrical transmission and line loss due to Joule heating.
Students will understand how electricity can be transmitted over long distances with minimized loss.
Students will follow instructions to build model transmission system to evaluate line loss
Students will utilize the engineering design process to optimize their systems.
Students will research alternatives to typical high voltage alternating current transmission.
MATERIALS
26 gauge bare nichrome wire
AA Batteries
AA Battery Holder with wire leads
24  resistors
Mini light bulbs
Mini light bulb holders
Wire leads with alligator clips
Temperature probe
Masking tape
Digital multimeter
Set up a model transmission system. You will use alligator clips with wires to connect a single battery in a holder to a resistor connected to the BNC wire that will be used as the test line, to connect the test line to the load (mini bulb in its holder), and to connect the load to the battery as shown in figure 1. Initially, do not connect the test line to the circuit. Instead, simply tape the alligator clips that will hold it to the lab table. Figure 1
Prepare the test line Leaving a 2 cm tail, coil the BNC wire around the temperature probe until there is a 2 cm tail on the other end. Figure 2
Connect one tail end to the resistor and attach the resistor to one of the alligator clips taped to the lab table. Then, connect the other tail end to the load using the other alligator clip.
Set the multimeter to voltmeter and prepare your timer and the temperature probe to collect data.
Record the temperature of the wire before you begin. Then, place the battery back in the holder and start the timer. Record the voltage across the BNC wire. Monitor the temperature of the wire until it no longer rises. At this point, stop the timer, remove the battery from the holder and record the final temperature. Figure 3
Calculate the change in temperature of the wire. You will vary the voltage by adding batteries to the circuit and record the time it takes for the same temperature change to occur.
Add another battery holder in series with the first. You will only need to remove one battery from the holder to interrupt the circuit between each trial.
Repeat step 7 with two batteries. Figure 4
Continue to repeat until all 6 batteries have been used.
Create a graph that reflects the dependence of heat loss on voltage differences. Figure 5
If time allows, manipulate a different variable to see what the effect on heat loss will be.
PROCEDURES
OVERVIEW
Students will learn about electricity transfer and power then will apply that understanding to experiment with the effects of varied voltage on electrical power loss. Students will research alternative power transmission in modern grids, devices and homes. A guided inquiry activity will prepare students to take their designs further on their own to develop and optimize a functional electrical transmission system. Students will conclude the lesson by researching alternative methods of transmission in the modern power grid. This activity should take approximately 2 days. The lesson will be presented on day one. A derivation and research will be assigned for homework on the night between the lesson and lab activity. Creating and testing the transmission systems will take the second day.
Figure 1
Figure 2
Figure 3
ENGINEERING CONNECTIONS
Working from instructions provided by the teacher, students will create their own power transmission system. Students should work in groups of 2 or 3. Students will work with provided materials and instructions to build a basic transmission set up. Then students manipulate voltage and other variables of their choosing to optimize power transfer. Students should consider the following engineering design process questions as they work:
How does it work? Derive an equation to describe the process.
Which components of the set up are variable? Identify the change that would result from modifying each variable.
What are the advantages of this set up?
How could the set up be improved?
Figure 4
Figure 5
LESSON OUTCOMES
Students will be able to explain what they have learned about high voltage power transmission, it’s limitations, current developments and applications within real-world situations. They will develop an equation that shows the dependence of heat loss on voltage in transmission lines. They will outline the ways in which commonly used alternating current systems vary from less common direct current systems. Students will list several challenges and benefits to both methods. Students will be able to apply their knowledge to solve College Board style free response problems.
REFERENCES
The Physics of Everyday Stuff: Transmission Lines:
Joule Heating:
Wires: