Physics Dept. Demonstration Manual

DEM36 - Electromagnetic Induction with Gilly Coils


To show that current is induced in a secondary coil by rising and collapsing magnetic field in the primary, adjacent coil.

  • Gilly coils, one c/w 5-way binding posts
  • Core rods; Iron, Aluminum, Brass
  • O.H.P. Galvanometer (100-0-100 uA Scale)
  • Tap switch
  • 6 volt battery
  • Banana-banana leads, one long pair
  • Spade-spade leads, 3 short


The secondary coil is connected to an overhead projection galvanometer. The primary coil is placed together with the secondary coil, and connected to a 6 volt battery and a switch. When the contact is made with the tap switch, the magnetic field rises in the primary, and cuts the secondary windings to produce a deflection on the galvanometer in one direction. Releasing the tap switch causes collapse of magnetic field in primary, also cutting the secondary coil. This results in opposite deflection on the galvanometer. Iron core is used between the coils to increase induction. Aluminum and Brass cores are used to illustrate their non-magnetic properties.