In this extension, student first study the properties of different kinds of materials, to see which ones conduct electricity and which ones are attracted by a magnet. They then use this information to design and make magnetic proximity switches, which are operated by bringing a magnet nearby. Materials that conduct electricy are called conductors, and those that are attracted by a magnet are called ferromagnetic.
The next three videos explore how to test and classify materials according to whether they are conductors, ferromagnetic, neither or both. The first shows how to test materials to see if they are conductors; the second tests them to see if they are ferromagnetic, and the third collects the data from these tests and organizes this data into a convenient data table.
The following materials are needed for the extension, in addition to those required for the main lesson:
small rectangular magnets
solid brass paper fasteners and brass-plated paper fasteners
Testing and classifying materials
What is a Magnetic Proximity Switch?
Like an ordinary pushbutton switch, a magnetic proxmity switch has two contacts, one fixed, and one that is springy so it will return to the open position when it is not being operated. The difference is in what makes these contacts come together. A magnetic proximity switch is designed so that when a magnet comes nearby, it pulls the springy contact against the fixed one, closing the switch and turning on a circuit. When the magnet is removed the movable contact springs back to the open position, turning the circuit off.
The next video shows how to select materials for making a magnetic proximity switch. Selection of materials depends on the classification of materials according to whether they are conductors and/or ferromagnetic (see above). The following video shows how to make a magnetic proximity switch using the materials that have ben selected. The diagram below the videos compares a magnetic proximity switch with a pushbutton switch.
Turning a pushbutton switch into a magnetic proximity switch
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