Jumping Ring (H22) [5K20.30]
Induction - LR Circuits
An iron core solenoid is connected to a 110 VAC variac. An aluminum ring is placed over the iron core of the solenoid. The voltage can be adjusted on the variac to make the ring levitate. The voltage can also be preset at a high level, so that when power is applied, the ring will shoot up toward the ceiling of the lecture hall. The ring can be immersed in liquid nitrogen and the demonstration repeated. The ring will be propelled a much greater distance. A second ring with a cut in its radius will not levitate. DC power can also be used. The ring will jump about 5 cm and return.
https://www.youtube.com/watch?v=CQ5abgQtye0
For DC: Plug the DC side of the switch into the resistor cage, and then hook up to DC power. When the power is switched on, the ring should jump once, not very high, before coming back down. The split ring should not jump at all.
For AC: Plug the AC side of the switch into the variac and then plug the variac into the wall. Start with the variac turned down low. It should be easily observable that the ring jumps much higher with AC than it does with DC. Once the switch is lowered, the ring will continue to levitate until the connection is broken. Increasing the current through the variac will soon have the ring jumping off the solenoid. The split ring should not jump at all.
Using liquid nitrogen, the ring may also be cooled, dramatically decreasing its resistance. This time, the ring should jump even higher than AC, and when the variac is turned all the way up, the ring should just hit the ceiling of 6-120.
Tags: 8.02, 8.022, Induction