Video: Watch this demo

UNSW Sydney Demo video

Description: This demonstration shows the basic function of a transformer. When the primary coil is connected to an AC power supply an altered voltage can be read read off of the secondary coil. Can show a step up or step down transformer (depending on which coil is primary).


  • 1000 turn coil
  • 500 turn coil
  • Variac power supply
  • Variac to banana plug cable
  • 2 AC voltmeters
  • 4 long banana cables
  • Induction C rod and L rod

Setup Procedure:

  1. Place the two coils on the Induction C rod, then clamp the L rod over the central post and tighten the screw
  2. Connect a voltmeter to each coil and set the meters to the correct range (Ex: 30VAC, Left, AC)
  3. Connect the Variac to the primary coil (Last step so that the professor can easily change between coils)

Demonstration Procedure:

  1. Check that each meter is reading the voltage of a coil
  2. Display the meters on the overhead projector.
  3. Turn on the Variac and slowly raise the voltage (don’t go above 30V!) Do not touch the coils when they are powered
  4. Note the voltage response of the coils
    – If the primary has fewer turns than the secondary, you should note the secondary coil has a larger voltage (Step Up transformer)
    – If the primary has more turns than the secondary, you should note the secondary coil has a lower voltage (Step Down transformer)
  5. Turn off the Variac, and switch the Variac leads to the other coil to try the other configuration
  6. When finished, turn off the Variac

Note: Calculating the theoretical step up or step down voltage on the secondary can be preformed using the # of turns of each coil, however coils are not 100% efficient in real life