Electric Energy Transfer Investigation - Day 2
Lesson 7 of 13
Objective: Students continue to investigate the transfer of electric energy into other forms of energy.
Today's warmup problem echoes one of the investigation stations and provides a way for students to put their recently-developed skills (the ability to employ Ohm's Law and analyze circuits) into practice.
While there are a couple of ways to resolve this problem, one successful path is to use the limiting current value (50 milliamps) with the battery voltage to calculate, via Ohm's Law, the total resistance of the circuit. As this is a series connection, the light bulb resistance can be subtracted from that total to find the value of R1 that will create the desired current.
Alternately, successful students calculate the voltage across the light bulb, leveraging the known current (again, 50 milliamps) and light bulb resistance. Once that voltage is known, it can be subtracted from the battery voltage to find the voltage across R1. Another application of Ohm's Law, this time focused on R1, will yield the proper value of R1.
Students work individually or in small groups while I circulate to provide targeted feedback or to help students unpack their thinking about this problem. After about seven minutes or so, I go to the board to facilitate a discussion about this problem. During the discussion, I invite students to share their thinking and to elaborate upon their approaches. While they share their ideas, I capture their thoughts at the board, for others to see. Even with a circuit as simple as this, multiple approaches can work. This is a great opportunity to encourage mental agility and to soften the desire - on some students' parts - for a fixed approach that can be memorized.
On day two of this multi-day activity, I want students to enhance their data-collection processes to increase data reliability and confidence. This frequently means systematizing their process to reduce human variations - arranging, say, the light sensor at a fixed distance from the light bulb.
Most teams spend the bulk of their time enhancing their data collection processes. We use a variety of measuring devices - a scale to measure changes in mass at the hydrolysis station, light and temperature sensors from Vernier at the light bulb and resistor-heating stations and, in an act of student ingenuity and motivation, a free app downloaded to a phone to measure decibels at the buzzer station. Some teams will begin to move beyond this phase and into the next stage of the process: converting their measured values into energy (or power). This often involves conversations with me; I can help students look for the right kinds of resources. For example, students involved at the buzzer station will need to think about converting decibels (or perhaps wave amplitude, if that's what they're measuring) to power and, furthermore, be reassured that sonic power can be compared back to electrical power.
Here is a photo showing general activity in the room. At this station, one can see the conversion of electrical energy into chemical energy through electrolysis bubbling. Here we can see the scenario for the small DC buzzer. Finally, these two girls are collecting data with the immersion heater.
We continue with the investigation, cleaning up with about five minutes left in class.
I ask some of the teams to submit to an interview. I want to know what they've figured out about their station and what improvements they've made to their data collection process. My goal here is to help to solidify learning though the act of active articulation. To do this, I choose a team that seems to be moving along effectively and interrupt their work. I tell them what I'm looking for - thoughts about their process and how it has improved - before turning the camera on and capturing their thoughts. Here's a student discussing the nature of his team's rotational motion station: