P. J. Ouseph
Physics Department University of Louisville Louisville, KY 40206
502 852 0918 Fax 502 852 0742
E-mail pjouse01@louisville.edu

Advanced Laboratory and/or Demonstration Apparatus

Apparatus Title: Faraday's Law Demonstration

Abstract: When a magnetically levitated rotor (a popular toy) is spinned, the magnetic field near it changes. This change can induce voltage in a coil placed near the rotor. The induced voltage can then be displayed on an oscilloscope to demonstrate Faraday's law.

Description Faraday's Law Demonstration

A popular science toy, , with a magnetically levitated rotor is the heart of this demonstration (Fig.1). A pick-up coil of about 1000 turns is kept a few millimeters above the rotor and the coil is connected to an oscilloscope. A 0.01-mF capacitor is connected parallel to the coil to reduce the high frequency background noise picked up by the coil and the connecting wires. The magnetic field in the pick-up coil can be changed by either spinning the rotor or producing an up and down oscillatory motion by pushing the free end of the rotor down a few millimeters. Induced voltage produced by the changing magnetic flux in the coil can be seen on the oscilloscope.


1. Position the rotor so that it is levitated above the base. 2. Spin or oscillate the rotor. (Low speed rotation gives a better signal). 3. To better view the induced voltage signal on the oscilloscope the following settings are used; volts/div, 5-10 mV and time/div, 50 ms.


The Faraday's law can be easily demonstrated by the equipment described here. Further, a discussion of the levitation of the rotor may be interesting for the students.