Physics Demo -- Jumping Ring

A solid metal ring is placed on an iron core whose base is wrapped in wire. When DC current is passed through the wire, a magnetic field is formed in the iron core. This sudden magnetic field induces a current in the metal ring, which in turn creates another magnetic field that opposes the original field. This causes the ring to briefly jump upwards.
If there is a cut in the ring, it cannot form current inside it, and thus will not jump.
When the ring is cooled in liquid nitrogen, the resistance of the metal is lowered, allowing more current to flow. This lets the ring jump higher. However, the magnetic field curves away at the top of the iron coil, meaning with DC power, the ring will never fly off the top.
When AC current is passed through the wire, the ring flies off the top of the iron core. This is due to the fact that the current lags the emf by 90 degrees in inductors (which is what we have here). This yields forces on the ring that are always pointing upwards, even as the current oscillates.
Original posting on MIT TechTV - techtv.mit.edu/...

[@Proeliator9]

No, the current inducted in the ring is always the opposite direction of the current in the coil, so the magnetic field of the ring always opposes the iron core's, and always is repelled. Think of the AC current demo, the current's direction is switching 60 times a second, but the ring only moves away from the coil.

[@DANYPATAGON]

Very good!, Faraday, Ohms, Ampere, Lenz, Lorenz, laws, explained in only one experiment!, nice.

[@robbie77300]

i suppose i said similar to what you said yourself. Although only a pure inductor has a 90 degree lag, as in an inductor with zero resistance or impedence. In practice thats not possible. Your right in that the ring will keep going up, as the ac current reverses, so does the induced current in the ring, so still opposes in the same direction

[@seagulljk2186]

So this actually happens 😮👏

[@MrScart1ssue]

As long as the metal ring is a conductor then it can have an induced current from a magnetic field, so yes. :)

[@my1987toyota]

would changing the A/C to a higher frequency propel the metal ring higher?

[@aritrakundu4726]

ye bruh

[@PashaSiraja]

@p3x797 of course !!
downwards ! that goes to the solid table, and absorbed ! =]

[@VideyoJunkei]

colder=less resistance and more current, I assume!!

[@ideasofcharan1383]

why dc can't throw the ring to air as ac can throw

[@TOMCLARKE08]

Thank you

[@AlbaxArcade]

And that is what you call a low powered rail gun

[@robbie77300]

well its not exactly accurate although close. When dc is connected you have an initial changing magnetic field- as the dc current rapidly changes from zero to full current flow, this change in magnetic field induces current in the ring and it jumps. But the dc current reaches a peak and is then steady non changing current, therefor can no longer induce current in the ring. In the ac current, the magnetic field is constantly changing, therefor current constantly induced in the ring, so keeps goin

[@Kanekighoull]

Hey there, thanks for explaining. Although I'm 11 years late and don't know whether you are reading this...

[@arianas7866]

@@Kanekighoull might've died

[@Kanekighoull]

@@arianas7866 who?

[@Kanekighoull]

@@arianas7866 this guy? Nah. I don't think so and why should I even think such things for a person

[@arianas7866]

@@Kanekighoull ok chill

[@stephenpprice]

awesome man

[@voled]

put more rings on it!

[@nmacgre]

Didn't know Jim went to MIT before starring in The Office.

[@PashaSiraja]

DC got owned by AC lol hahaha
rapid-fire !!!
xD awesome demo thanx !!
=D

[@AngeK47]

i have a question. if you change the direction of current would the ring be attracted to the coil because you are changing the direction of the magnetic fields?

[@Ashish-px5fi]

Here the principle is that the coil would like to resist the change in flux.

[@ssslawek]

what voltage of AC and DC. The same? was the ring frozen whem you applied AC?

[@harkiratsingh3056]

what shoud be the voltage in ac current to make the ring jump out

[@ClayAlchemist]

@pashaahsj LOL.
Amazing. I love learning new things every day.

[@omnipotentfish]

cool!!!

[@colt4667]

I bet you can really impress the chicks with this demo. Seriously.

[@reginaphalangi3797]

Thanks🌺🌺🌺🌺🌺✨

[@The72challenger]

So that's how the lunar module escaped the moon...

[@TimsVideoArchief]

can i play in your lab one day???? can i, can i, can i, can i????

[@Scelenaarwen]

power source : AC/DC
Alriight :D

[@realknow007]

❤️❤️

[@fpsmanager]

Eddy Currents yei boi

[@nutcake95]

lawl AC DC power :V

[@oiimadweeb5292]

hoh

[@oiimadweeb5292]

good 1