Aluminum Can Polarization Notes

The Aluminum Can Polarization Interactive is an adjustable-size file that displays nicely on smart phones, on tablets such as the iPad, on Chromebooks, and on laptops and desktops. The size of the Interactive can be scaled to fit the device that it is displayed on. The compatibility with smart phones, iPads, other tablets, and Chromebooks make it a perfect tool for use in a 1:1 classroom.

This Interactive is intended for use near the early stages of a learning cycle on charge, charge interactions, and charging methods. The Interactive targets the concepts associated with the polarization of conductors by a charged object. Learners can select either a glass rod or a rubber rod and drag it near to an aluminum pop can that is at rest on a surface. The Interactive simulates the movement of the can. Once the Show Charges button is pressed, learners can view the movement of electrons within the conducting can. Electrons are attracted to the positive rod and repelled by the negative rod. As the rod is moved around, electrons respond accordingly.

It is important to note that there is never any movement of positive charges within the conductor. Protons - the source of positive charge in atoms - remain fixed in the nuclei and are unable to reposition themselves. The presence of a nearby negative object induces electrons in the can to move away, leaving the side of the can nearest the negative object with the original protons.

It is also important to note that the aluminum can is not a charged object. While it contains charges, it does not have an overall charge. The number of positive and negative charges is equal. This balance of the two types of charges is evidence that the aluminum can is neutral. As the charged object is brought near the aluminum can, the positive and negative charges are separated from each other and the can becomes polarized. This polarization - or separation into opposites - is induced by the presence of a nearby charged object and explained by simple rules like opposite-charges attract and like-charges repel. In saying "opposite charges attract", we would mean that the positive glass rod attracts the negatively-charged electrons within the can. This is what causes the can to become polarized. In saying "like charges repel", we would mean the the negative rubber rod repels the negatively-charged electrons within the can. This is also causes the can to become polarized. In both instances, the polarization of the aluminum can causes it to be attracted to the charged rod. The basis for the attraction between charged objects and neutral objects is the polarization of the neutral object.

The physics being simulated in this Interactive is easily demonstrated within the classroom. The Physics Classroom urges teachers to acquire a conducting pop can or soup can and to give it a try. Place the can on a desktop, charge an object, and bring it near the can. Show the demonstration to students before the use of the simulation and give students a chance to offer explanations as to what is happening at the particle level. The Interactive will help to inform their answers.

The Physics Classroom has prepared one activity for use with this Interactive and encourages teachers to use it with their classrooms. The activity is a very open-ended activity that culminates with students constructing an electron density diagram in which they shade in the region of the pop can where electrons congregate most densely. View the Activity.
 

There are numerous resources at The Physics Classroom website that serve as very complementary supports for the Aluminum Can Polarization Interactive. These include:

 

Additional resources and ideas for incorporating Aluminum Can Polarization into an instructional unit on electrostatics can be found at the Teacher Toolkits section of The Physics Classroom website. Visit Teacher Toolkits.