PIRA 5J10.20: Inductance: DC Back EMF
Instructions / Notes:
- A large 3 Henry inductor is connected in parallel to a 37 volt DC light bulb circuit using the large knife switch which is at the center of this circuit board.
- The circuit board is really two demos on board. Only one side of the circuit board is the DC Back EMF demo.
- With the 3 Henry inductor connected to the circuit - the bulb glows dimly until the small knife switch is opened.
- At this point, as soon as the small knife switch at bottom portion of the demo is opened - the magnetic field of the inductor collapses and bulb flashes brightly for a brief moment.
- Also notice the arc/flash that occurs at the small switch at the moment that it is opened.
- If the large the knife switch in the center of the circuit board is opened - then all you are left with is a 37 volt DC light bulb circuit.
- Once again - when the center knife switch is in the opened position - the coil is no longer connected to the circuit board.
- With the center knife switch in the open position - the light bulb will exhibit a normal on/off behavior when the smaller knife switch is opened or closed.
- In other words - no brilliant flash is observed, when opening the small knife switch, if the inductor is no longer part of the circuit.
- 5K10.40 the Iron Core in Mutual Inductance demonstration is a good companion demo to show another example of a back EMF produced by a collapsing magnetic field around an inductor.
Last Updated 03/2018 - University of Texas at Austin Physics Department - All Rights Reserved