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Lodge's Experiment

Sir Oliver Lodge's experiment demonstrating the first tunable radio receiver was an important stepping stone on the path toward the invention of a practical radio.

In 1894 by English physicist Sir Oliver Lodge demonstrated the key principles behind the invention of radio, which was then called wireless telegraphy.

An electric circuit created in the transmitter generates electromagnetic radio waves that are picked up by the receiver.

Instructions

  1. Take a close look at the setup. On the upper left, the transmitter consists of a Van de Graaff generator and a Leyden jar, looped in a circuit broken by a spark gap. The electrodes of the Leyden jar are connected to an adjustable metal loop. The Leyden jar is a capacitor and the adjustable metal loop is an inductor, a coil of wire that generates a magnetic field when current is passed through it. The inductor and capacitor together form a parallel circuit.
  2. On the lower right is the receiver, consisting of another Leyden jar capacitor connected to a metal antenna loop. The circuit also contains a neon bulb.
  3. Notice that current from the generator produces enough voltage to jump the spark gap and charge the Leyden jar. Adjust the spark interval to create sparks faster.
  4. When the spark jumps the gap, you’ll see it makes the receiver’s bulb light up. That’s because the transmitter loop generates electromagnetic radio waves. Those waves travel to the receiver and cause an electric current on the receiver’s antenna loop. The antenna loop then charges the Leyden Jar until enough charge is built up to flash the neon bulb.
  5. By moving the loop position slider, you can tune the transmitter to find the resonant position that will produce frequencies most detectable to the receiver and produce the brightest flash from the bulb.