Drifting Into Current

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Objective

Students will be able to define drift speed & current in terms of charge movement over time.

Big Idea

Students discover the definitions of current and drift speed in a reading exploration activity.

Context

After describing interactions between charges and the properties of electric fields, today's goal is to introduce students to the effects of charges that flow. In shifting our thinking to the movement of electrons, students are able to define current and drift speed (HS-PS3-5). The lesson starts with a review of electric fields on a ranking task before students engage in a reading exploration activity (SP8). The lesson closes with students applying their new knowledge with collaborative problem solving (SP5).

Introduction with an Electric Force Ranking Task

10 minutes

When students walk into class, today's ranking task is already projected onto the screen at the front of the room. I choose this task because it asks students to apply their knowledge of electric force, specifically how different charge configurations impact the force on a test charge. The task is meant to refresh students' thinking about material learned during the previous class.

Once the students are settled, I read the instructions from the top of the activity. My reading of the instructions is to ensure students understand that class has started. I emphasize to students that they should work individually and take about five minutes to rank the configurations, explain their reasoning, and then assess their level of confidence. During these five minutes of work time, I walk around the room and informally assess how students are doing with simple glances at their work. My changes in location help students stay quiet and focused.  

When the five minutes are over, I reveal the answers to the students by writing them onto the front screen: D, C, A, F, E, B. I then ask if anyone got all of the answers in the correct order. This student has the right answer and is willing to share with the rest of the class. She starts by highlighting the fact that each test charge has the same magnitude and the surrounding charges also have the same magnitude. Then, she explains that electric force is directly proportional to the magnitude of charge and inversely proportional to distance (squared). After she completes her explanation, I end the introductory activity by asking if anyone requires further clarification. Because this activity reviews material from the previous class and the goal is to review that knowledge, the students keep their work to use as a resource when studying for the unit test.

Current & Drift Speed Exploration Activity

30 minutes

After our whole-group introduction which allowed students to activate their prior knowledge of Coulomb's Law, the goal of the rest of this lesson is to define current. I now allow students to choose a partner and take a computer from the cart at the front of the room. We use MacBook Pro's in my district and each department has a cart that can be shared. At this point in the year my students are familiar with the organization of the computers and cart. I decide to let students choose their partner since I want them to be comfortable and focus on internalizing today's material.

As the computers are booting and after students have pushed their desks together with their partner, I give each student a copy of the current exploration activity. This document is a guideline that helps students identify the absolute minimum material they should record into their physics notebooks. Once they've opened the document, the students follow the link to the Electric Current Section of the Physics Classroom. At this website and still in their pairs, students read through the text and use the document to guide them through the goals of understanding on the activity sheet. I let students know that they can read aloud or individually, but the point of them being in pairs is to discuss and determine the most important parts of the text.  

While students are working, I walk around with the answer key to ensure they are actively engaged in the learning process. To me, this means that they are on the proper website, reading or discussing some component of work, and writing down a thorough set of notes. When I walk around, I spot check their written work and engage students in questions such as "Is conventional current based on positive or negative charge carriers?" or "Did you have any idea that drift speed would be so slow?"

As students finish reading, they are able to move into the next part of the lesson and apply their new knowledge. This activity gives the foundation of the current and drift speed concepts, and the closure of this lesson allows students to practice application of these new concepts with collaborative problem solving.

Current Collaborative Problem Solving

10 minutes

As closure and an informal assessment, students have the rest of the class to start tonight's homework. This homework assignment allows students to apply information from the reading exploration activity. Specifically, students use the current equation (I = Q/t) to solve for missing quantities. A few of the problems require students go a step further and find the number of electrons that flow past a point in a given amount of time.

Students remain with their partners from the reading activity as I pass out a copy of the homework to each student. This is an assignment that needs to be completed by each individual on a separate sheet of paper, although they may use their partner from the previous activity as a resource while working in class. I encourage collaboration, as students apply their new knowledge for the first time. 

Also, I walk around to offer help or problem solve with the students as they are working. You might hear me say "What units should time be in?" in response to a student asking about an answer that doesn't make sense. My style is to lead the students to the answer, not just provide it for them. That being said, if a student is continually struggling and in obvious need of being shown the answer, I accommodate him or her.  

I call the homework informal because I don't want students to get nervous that it counts as a quiz or test grade. Since my goal is to assess their level of understanding, I collect and grade the assignment for accuracy at the start of the next class meeting. Not only do I want to give students personalized feedback on this homework assignment, I also want to check the pacing of the course and make sure my students are ready to move on to the next lesson.

This is our closure activity for today. Most students are able to get the first three problems completed before the end of class. I am also trying to take a step towards a flipped classroom. I like students to have me as a resource when they work through problems, and I think it helps them build confidence. In the past I've attempted to do entire class periods of a full flipped classroom, but it's hard to hold the students accountable for digesting the needed material. I find that a combination of work time (that lasts right up until the bell rings) and in-class learning best fits the needs of my students.