Demos: 6B-05 Magnetic fields from Different Current Carrying Configurations

This demonstration has four devices consisting of heavy copper wire threaded through a clear Lucite plate for overhead projection. The different devices are: single wire; single wire loop; solenoid; toroid. When a large DC current is passed through each device, iron filings sprinkled on the plate show the magnetic field lines that are created.

Directions: Place the apparatus on the overhead projector and adjust it so that the plate surface is in focus. Turn on the power supply. Begin sprinkling iron filings on the plate, watching carefully while the pattern develops. Tapping the plate periodically helps. As soon as you see a fully developed pattern emerge, stop sprinkling the filings because too many filings cause the pattern to be smeared and indistinct. PLEASE NOTE: Adjust the VOLTAGE VARIAT Setting to Maximum to get the best results for the single wire and single wire loop. When you have the desired pattern, please turn off the power supply to avoid any possible damage to the power supply.

Suggestions for Presentation: For optimum effectiveness, we suggest that you show the single-loop pattern from first. Then let the students think about what happens to the pattern as more loops are added. Next place the solenoid on the overhead and show the pattern. Accompanying this demonstration is an overhead transparency showing the field pattern for a single bar magnet. Point out the similarities. The solenoid behaves like a bar magnet, but it can be turned on and off, has many industrial and home applications. One is the solenoid in the starter motor of an automobile. A cut-away of a real starter motor is available to be shown to the class. Finally ask the students about bending the solenoid into a circle and think about the kind of pattern that might emerge. Then set up the toroid and show the field pattern with iron filings as before.

Applications: Relays of all sorts, giant electromagnets used in scrap metal yards, telephone speaker and earpieces.

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