Electromagnetic Ring Launcher -- Building a Science Museum Classic

The Jumping Ring or Electromagnetic Ring Launcher experiment is a staple of science museums and physics class rooms. Here's how to build your own right in your home.

There's a very common demonstration in  science museums and physics-classrooms called the “Jumping Ring” or “Electromagnetic Ring Launcher." The experiment involves a several centimeters long cylindrical iron core inserted in a large solenoid and a copper ring runs through the extended iron core. When the solenoid is powered by the AC mains, the ring jumps out of the core.

There are various reasons for the experiment being so popular and so significant in science and engineering. Firstly, it is interesting to observe a metal ring jumps out or hover. Secondly, it utilizes Faraday’s law of induction, Lenz’s law, mutual inductance, and forces due to electromagnetic induction to make it possible for the ring to hover or jump. The main problem with this type of conventional ring launcher is its bulky size and weight, as it requires a large number of turns of thick copper wire for the solenoid and heavy iron core inside. Furthermore, as it operates at the mains-line voltage (115 V or 230 V, AC),it is not safe to operate. Calculations show that the launching of the ring is many times more efficient at frequencies several times higher than that of the AC mains (50/60Hz).

In this project I used a square wave generator of adjustable frequency from 700 Hz to 18 kHz employing a 555 timer IC; the output of which drives a power MOSFET. The MOSFET drives a small coil of ~50 – 60 turns wound on a 10 cm long ferrite cylinder instead of an iron core. A copper ring is placed through the extended part of the ferrite cylinder. A 16 micro Farad film-capacitor is placed in parallel with the coil to achieve parallel resonance. At resonance the current through the coil can be achieved several times higher than that is supplied by the power source. Using a thick copper wire (AWG #14) for making the coil, the coil-resistance is lowered, which makes the quality factor (Q) of the coil high. High Q of the coil maintains nearly ~ 8 times higher current than the power supply can provide. The high primary current is essential to induce high current in the coper ring, the interacting field makes the ring levitate. The circuit needs only 24V DC do levitate, hover and shoot the ring. A 10-Ohm resistor is used in series with the 24V power supply, as the frequency of the oscillator is slowly increased, supply current goes down gradually. At resonant frequency supply current reaches to minimum, (~1.2 A), and also at this point the copper ring levitates and hover midway on the extended ferrite rod. Another switch is used to short the 10-Ohm resistor, when it is shorted, the ring jumps few centimeters out of the rod. Now, keeping the 10-Ohm resistor shorted, if the power supply is turned ON, the ring jumps tens of centimeters above the rod. This video shows these effects.


Full build instructions and parts list continue below: 

The circuit:

The circuit consists of a square wave oscillator implemented by a 555 timer IC, a power MOSFET and a MOSFET



Because of the parallel resonance, much higher current is circulated in the LC circuit compared to the current taken from the power supply. For instance, at resonance the current taken from the DC (24V) supply is around 1.5 A, however the current in the coil is ~12A. High current is essential to levitate the ring. Higher primary current causes higher current in the ring, resulting in higher upward force on the ring.


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