MIT Physics Demo -- Back "emf" in a Large Solenoid

[rafaelrosad2387]

Nice vid..keep up the good work... 

[GreenLearning]

I just love this kind of thing! Who said bigger is not better? LOL

[thewii552]

I dare you to lick it

[callmeshane303]

If you earth your power using copper contact patches on the outside of each testicle, you will know the power of Jesus to protect you from the adversary.

[D34Df007]

that was some epic emp

[coldarc]

the iron core act as a capacitor by generating a strong magnetic field that causes an induction current in the copper wire after the power become disconnected. its like short circuit a capacitor after it have been charged.

[freemanx2x]

Its funny to see people actually really believe that they understand in minute details what is really going on here..."collapsing electro-magnetic field"...is like you say "water is wet"...

[OnnomonnomonnO]

I can hear a humming of  AC ..but anyway...what is an input voltage?

[camelsonhorizon]

pause right at :17 and see the man on both sides of the screen. eery. back emf overunity bedini machines, look it up.

[D34Df007]

@camelsonhorizon thats a little video artifact called "tearing". It probably happened because of either the sudden bright flash that lasted less than a single frame (which can 'confuse' the recording device) or because of the EMF disrupting the camera and causing the recording device to overlap frames.

[Otari33]

TIme taken to build magnetic field versus time taken to collapse magnetic field. Knife switch closes coil charged in nanoseconds, knife switch remains closed for about 5 seconds? Coil still charging during this time.. will never reaches full charge even if left forever. Knife switch opens, five seconds of charging is released in nanoseconds.. energy is not created or increase... just converted faster ... time is the factor here lads.. thankyou for your attention

[m1ndcontroller]

THAT'S NOT BACK EMF !!!!

That is the voltage spike from the collapsing magnetic field!!!!

Back electromotive force only occurs when the current is turned ON!!!!

Is this the best MIT has to offer??

I'm glad I saved my $100,000.

And you shitheads have the audacity to scoff at the free energy experimentors?

MIT.. YOU SUCK!!!!!!!!!!!!!!!

[bardfinn]

That would be the collapsing electro-magnetic field creating a voltage spike because the collapsing electro-magnetic field /is/ the emf.

[tonyrueb]

first and for most... name calling is not nice, second cursing is not nice, third, nothing sucks in science, there is just high and low pressures, fourth, caps are annoying. fifth, free energy is in direct violation of the law of conservation of energy, until you can prove that this law is incorrect, or has exceptions, free energy will not be accepted by the academic world, only the uneducated with to much time.

[alfabitsoopify]

@tonyrueb Nothing sucks in science? Vacuums?

[tonyrueb]

@alfabitsoopify - good question a Vacuum is nothing more then low pressure with high pressure pushing in to fill the space. the forces is more of a push not a suck (or a pull)

[alfabitsoopify]

@tonyrueb Im aware just making a joke. :]

[wowsa0]

Back emf is the term used to describe the emf which occurs as a result of a current acting on itself which always acts in the opposite direction to the rate of change of current. This video is a perfect example of back emf.

[electrostatic1]

Physically, the magnetic fields in the inductors hold potential energy. The inductors can not maintain a magnetic field in the absence of current. When the switch is opened the fields "collapse", pushing electrons as they do. (The protons are also pushed against, but they can't move.) The charge imbalance caused by pushing all of the free electrons to one side of the coil is "voltage". If the spark was not able to short out, the energy would have bounced in the coil and been radiated as RF.

[teslaandlyne]

The voltage flips directions to keep the current in the same direction. i = L dv/dt the v changes direction (giving a minus sign ) and decays (giving a minus sign) so i stays the same at instant t and decays.

[teslaandlyne]

That was so hot and bright the action caused a flame. There is an experiment putting high frequency through a candle flame that set up a tree of carbon nano particles.

[teslaandlyne]

The coil current must remain the same or constant at t- and t+ of the switch open time of t. To do this the voltage ups to air breakdown potential and dissipates the energy into the air. The air capacitor thus forms and RLC circuit and perhaps exhibits oscillations as "a Leyden jar magnetized needles in alternating layers" as a discharge is an oscillation. (page 226 Whittakers Vol 1 "History of..Electricity") Tesla seemed to always have circuit breaks to set up voltage and frequency.

[codygillespie]

I believe it is inaccurate to call this back emf. Back emf occures when you turn the power on, not off. Look up the bemf definition. This is a collapsing magnetic field.  Its the start of what tesla refered to as radiant energy, which he studied deeply in colorado springs.

[muchadoaboutnothingg]

Back emf is the voltage that pushes against the current which induces it.

The solenoid created a back emf to act against the gigantic drop of current, the voltage was so large that it causes an electric breakdown in air.

Correct me if I'm wrong.

[codygillespie]

Point taken. I understand what you are saying, but i was referring to the lack of back emf on its way out. Back emf occurs when the switch is closed due to lenz law. It takes a while for the current to build, following a ramp curve due to back emf. However it takes a very short time for the field to collapse when you open the switch because lenz law and back emf dont really apply in an open circuit. With no opposing force the initial current turns to almost pure voltage on its way out.

[muchadoaboutnothingg]

wasn't the circuit closed by the breakdown?

and ah, V=IR, if V is really very large, there must be a current right?

[codygillespie]

Correct in this situation it was closed by the arc. And yes there was a current too, as voltage and current are inversly related, so higher voltage equals less current. This can occure without the arcing closure such as conditions of capacitance, but the point is the situation created a condition where an opposing force (bemf) isnt present to restrict the the collapsing field, with no opposition the initial current applied is transforms into mostly voltage. This is how i understand it anyways.

[codygillespie]

Perhaps what im trying to convey could would be easier to understand by observing how long the core takes to saturate verse how long it takes for the field to collapse. Bemf is what causes the delayed saturation, while the lack of bemf allows the very fast collapsing field. What do you think?

[EnergyTechnologyNow]

I show in test more energy out then in.

[EnergyTechnologyNow]

I agree, my pulse generator show how much energyis produced.

Look at some of my videos.

I have over 300% efficiency coming back from emf.

[electrique527]

How and what did you measure?

Do you actually know what happens when you get to 300%?

Just connect your output to your input.

If you can still read this afterwards, then it was no 300% , and most likely substantially below 100

:D

[EnergyTechnologyNow]

My testing on the pulse generator shows more energy out then in.

the testing is on youtube.

[EnergyTechnologyNow]

Back emf is what happens when the power is turn off, the forward emf is when you turn on the power.

There is greater energy coming back then what is going in to the coil.

[AEVector]

Codygillespie, is correct. Back EMF is the effect on incoming current when the power is turned on, NOT when it's turned off. Inductive kickback or flyback effect is what happens when power is turned off. Back EMF is what opposes the initial current flow through a coil. The higher the inductance the greater the opposition to initial current flow and the higher the back EMF.

[crippled82]

"back" is just relative to the direction in which current is changing. Flyback is also back emf, the current instantly changes to zero.

my 2 cts :

[electrique527]

Define: "energy" please