Al Tobias (wat4y) - Office: Gibson S123 & Physics 218, (434) 924-0538
Demonstrations are cataloged according to PIRA Bibliography
PLEASE REQUEST DEMOS WELL IN ADVANCE
Due to Physics Building renovations, the lead time to set up demo requests has increased due to the need to transport equipment across campus. Please be kind and let me know well ahead of time what you need.
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video - Back EMF in an Inductor
Purpose:To show that a very large back EMF is produced in an inductor when the current changes rapidly.
After the electromagnet has been energized, the knife switch can be opened and a large arc can be observed. Be very cautious of the high voltage and heat of the spark. Main spark is produced at break rather than make.
Hints:The electromagnet coil pair has a measured inductance of roughly 3 Henries and wire resistance of 15.7 ohms.
For more information on high voltage sparking when a current carrying inductor is suddenly cut off from its power source, see Giancoli, Physics for Scientists & Engineers, 4th Ed., Chapter 30, Problem 27.