# Reviewing Electrostatic Charge Stations

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## Objective

Students improve charge diagrams based on their observations at a variety of electrostatic charge stations.

#### Big Idea

Charge stays in place on an insulator and charge is free to move around on a conductor.

## Context and Supplies

In the previous lesson, Charge Stations, students students rotated between 7 stations where the primary objective at each station was to observe the behavior of the charged objects at each station and draw a charge diagram based on that observation.

This lesson, students look at the common misconceptions and mistakes that their peers made and fix their own charge diagram if needed.

Applied NGSS include Science Practice 1: Asking questions about their observations and Science Practice 2: Developing and using models where students draw charge diagrams. As we review the common mistakes, students use Science Practice 7: Engaging in argument from evidence and CCSS Math Practice 3: Construct viable arguments and critique the reasoning of others. This is all in the context of NGSS performance standard HS-PS2-4: Use mathematical representations of Newton’s Law of Gravitation and Coulomb’s Law to describe and predict the gravitational and electrostatic forces between objects.

To prepare for the class, I use a document camera to take pictures of student work, some that contain misunderstandings and some that are exemplary. I have a projector that displays the student work on the whiteboard for students to see.

## My Favorite "No" Charge Diagrams

25 minutes

I pass back the students charge diagrams that were made during the Charge Stations lesson. To prepare for the class, I took pictures of student work that contained mistakes or misunderstandings as well as exemplar work. We spend most of this period in review of the student work and students correct their own sheets.

The review is done with My Favorite "No". This is a strategy where we look at a student sample that shows misunderstandings or mistakes. I find a sample work that includes a common mistake or misconception. It is important to start off My Favorite "No" by having students point out what is right with the sample and which aspects of the student work demonstrate understanding of the content. After that, I ask students to point out what could be done to improve the work.

Here are examples of My Favorite "No".

Station 1:  The can quiver where a charged plastic tube moves an aluminum can.

I get answers such as, "The plastic tube has charge in one spot which make sense since it is an insulator" and "The tube and can have opposite charge which is why the can is attracted to the can".

How can we improve this work? "The can should not have a net charge positive charge, but should be neutral". Or "The can should be polarized".

Station 2: Packing peanuts where a charged tube is used to pick up packing peanuts.

I get answers such as, "the tube has a net charge" and "The packing peanuts stay neutral".

Areas of improvement include, the tube should not have charge spread all around it but should be localized in the areas where the rabbit fur was rubbed. Also, the packing peanuts should be polarized.

Station 3 - Rub two hanging balloons with rabbits fur to charge them up. This causes the balloons to repel.

I get answers such as, "The balloons have the same charge, which is why they are repelled".

Areas for improvement? The charge on the balloons should not spread evenly out but will be localized only on the areas rubbed by the rabbit fur.

Station 6 - Water deflection due to charge balloon.

I get answers such as, "The water is attracted to the balloon" and the "balloon has a net charge that is local to where it was rubbed with the rabbit fur".

Areas for improvement include "The water does not have a net charge" and "The water should be polarized".

Station 7 – Electroscope: an electroscope, rabbit fur and a plastic tube

I get answers such as, "Charge is separated between the top and lower part of the electroscope" and "Like charge is on the leaves which is why they repel each other".

An area of improvement is that the negative charge on the tube repels electrons. So the charge distribution on the electroscope should be flipped with negative on the bottom leaves and positive on the top ball.

## Exemplar Charge Diagrams

10 minutes

After we are done with My Favorite "No", I show a collection of exemplar work. While we go through the mistakes, the expectation is that students fix their own work. Now I display Student Work - Exemplars so they can see if they have accurate charge diagrams. I answer any questions the students have and give the class a few minutes to make the necessary corrections before I recollect their work to make sure they correct their mistakes.

## Lightning Charge Diagram

15 minutes

To finish the period, I instruct students to create a 4-panel charge diagram of a lightning strike. This is an amazing occurrence in nature and is directly applicable to the content we are studying; this is a great exercise for students to engage in

Students are free to use their smart phones or the classroom computers to look up the information they need. It is not hard to find information through a Google search with the words: charge diagram and lightning strike. This search gives a variety of high quality resources for the students to use. The Lightning Charge Diagram is a sample of the work produced by the students.

Now that students have developed a model via the charge diagrams of how charge behaves and flows, the next lesson introduces Coulomb's Law which quantifies the electric forces involved between charges. Students are to read College Physics text on Coulomb's Law and take notes on the material. They should understand the application of Coulomb's Law and I suggest they work through some of the sample problems. I am to prepare my students for college and I tell them that this is a college level assignment as I expect them to learn this material on their own and be ready to show their understanding.