3B10.77 - Aliasing

Code Number:
3B10.77
Demo Title:
Aliasing
Condition:
Excellent
Principle:
Frequency Modulation
Area of Study:
Acoustics

Disclaimer

Equipment:
Large DC Motor, Strobe Light, Painted Pulley, and LabQuest Mini Interface with Photogate.
Procedure:

Set the rotation rate of the motor as near to 1000 rpm's as possible.  The LabQuest Mini interface must be used for this demo if you wish to continually monitor the rpm and rps.  Use the LoggerPro program "Tachometer" to monitor this (Note: The "Tachometer" program is set so that it counts each break of the photogate by the spokes of the pulley wheel and then divides by 6 which gives the true rpm's of the motor).  Set the flash rate of the strobe light to the same rpm setting of your motor.  When both are running the pulley of the motor should appear to stand still.  By increasing the strobe rate to several Hertz above the rpm rate of the motor, the pulley will appear to slowly turn in the clockwise direction.  When you decrease the strobe rate to several Hertz below the rpm rate of the motor, the pulley will appear to slowly turn in the counter clockwise direction.

NOTE: The LabPro interface can be used for this demo but will only allow you to monitor the rpm's of the wheel for 3 to 5 seconds before the program will stop due to buffering problems.




Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.