Will spinning a magnet at 6000rpm create a 100hz radio broadcast wave?

[BrianHG]

Ok, ignoring the difficulty here, and assuming the magnet's north and south pole is sufficiently wide apart to create an antenna tuned to 100hz, you can see why spinning this monster would be absurdly difficult due to length, and ignoring the hardware and location needed to spin the massive thing and G-force which would break the magnet at that length and speed, (I know how any forum member here can easily pick this scenario to pieces...) would this rotating magnet create a 100hz electromagnetic wave?

[IanB]

I can see the spinning magnet helping to create the magnetic part of a wave, but where would the electro- part come from? I think there needs to be an electric field as well as a magnetic field to construct an electromagnetic wave.

[RoGeorge]

...would this rotating magnet create a 100hz electromagnetic wave?

Yes.

[MrW0lf]

And yes it is, investigate how MRI works, wobbling little proton-magnets around:

[tom66]

I think this is the same idea that if you were able to create a circuit that oscillated at 400 THz, would the wire glow red?  Yes.  But good luck doing that with anything similar to actual electronic components.

[BrianHG]

I think this is the same idea that if you were able to create a circuit that oscillated at 400 THz, would the wire glow red?  Yes.  But good luck doing that with anything similar to actual electronic components.

Don't LEDs or laser diodes do this?

[BrianHG]

And yes it is, investigate how MRI works, wobbling little proton-magnets around:

Looking at the MRI, as that video is presented, it's like the MRI primary magnet is aligning the water molecules orientation, and using an added injected em RF signal to vibrate them, then listen to the signal they make as they return to alignment to the main magnet.  At this scale it is still difficult to imagine a powerless magnet just spinning in space creating my described 100hz radio wave.

It's comes to me as a 100hz AC generator core, but, without an electrical loading coil, how long would this magnet spin in free space in a vacuum.  Or, will the generation of the field itself slow down the rotation even though there may not be any close metal/coil load to create drag like in a generator.

[RoGeorge]

It's not the water who's aligned, it's the protons inside the Hydrogen atoms. While that video is correct, it makes no sense unless one already knows how MRI works. Also, MRI is a complex mix of physics phenomena and signal processing technologies, let's forget about MRI for the moment, it will just add confusion to the topic. Let's stay with our rotating magnet.

Yes, the rotating magnet will slow down "by itself", because the rotating magnet is generating radio waves, and radio waves carry energy.

[Ian.M]

Amazingly enough, the pioneers of commercial radio were able to get up to 100KHz and powers of hundreds of KW by mechanically varying the magnetic field.  They used a spinning slotted steel disk to vary the reluctance of the magnetic path, because materials strength issues made it impractical to spin magnets fast enough.
https://en.wikipedia.org/wiki/Alexanderson_alternator

[fubar.gr]

I can see the spinning magnet helping to create the magnetic part of a wave, but where would the electro- part come from? I think there needs to be an electric field as well as a magnetic field to construct an electromagnetic wave.

If you generate an alternating magnetic field, the electric field component of the wave emerges on its own.

Similarly, most dipole antennas generate only the electric component. The magnetic component emerges from the electric one.

[Ampera]

I can see the spinning magnet helping to create the magnetic part of a wave, but where would the electro- part come from? I think there needs to be an electric field as well as a magnetic field to construct an electromagnetic wave.

If you generate an alternating magnetic field, the electric field component of the wave emerges on its own.

Similarly, most dipole antennas generate only the electric component. The magnetic component emerges from the electric one.

That means if you get a magnet spinning, you can harvest free electricity from it! Infinite energy is possible, kappa.

[Zero999]

I can see the spinning magnet helping to create the magnetic part of a wave, but where would the electro- part come from? I think there needs to be an electric field as well as a magnetic field to construct an electromagnetic wave.

If you generate an alternating magnetic field, the electric field component of the wave emerges on its own.

Similarly, most dipole antennas generate only the electric component. The magnetic component emerges from the electric one.

That means if you get a magnet spinning, you can harvest free electricity from it! Infinite energy is possible, kappa.

To harvest electricity from the spinning magnet, you need a coil near it, which will generate an alternating magnetic field, opposing the spinning magnet, just slowing it down.

[Ampera]

I can see the spinning magnet helping to create the magnetic part of a wave, but where would the electro- part come from? I think there needs to be an electric field as well as a magnetic field to construct an electromagnetic wave.

If you generate an alternating magnetic field, the electric field component of the wave emerges on its own.

Similarly, most dipole antennas generate only the electric component. The magnetic component emerges from the electric one.

That means if you get a magnet spinning, you can harvest free electricity from it! Infinite energy is possible, kappa.

To harvest electricity from the spinning magnet, you need a coil near it, which will generate an alternating magnetic field, opposing the spinning magnet, just slowing it down.

then all you need to do is put the energy from the coil and place it into a motor that will spin the magnet. b00m, problem solved. take that facts and actuality.

kappa

[MrW0lf]

I went to the woods and while harvesting mushrooms thought occurred: Antennas are impedance matched to "free space". This is what gets stuff out. Now for magnet to "slow down" it must also impedance match to something. Simple with loaded coil but what about original case of floating in "free space". Perhaps magnet should be subjected to some additional accelerations besides steady spinning to match with "free space"...

[IanB]

Perhaps magnet should be subjected to some additional accelerations besides steady spinning to match with "free space"...

Except anything spinning is already accelerating. An object spinning at constant speed is under constant acceleration. This is why a spinning magnet can emit radiation, whereas a magnet moving at constant speed in a straight line cannot.

[MrW0lf]

Constant acceleration is puppy compared to jerk
https://en.wikipedia.org/wiki/Jerk_(physics)

[StillTrying]

In the case of a spinning magnet in free space where does the angular momentum go?

[technix]

Adding a question, what is the optimal size of a magnet that can be bolted to a 6000rpm motor for this? (I hope 1/2 or 1/4 wavelength can work...) What about one bolted to a 15000rpm SCSI hard drive spindle motor?

[IanB]

In the case of spinning magnet in free space where does the angular momentum go?

If a spinning magnet emits radiation then the radiation carries energy away with it, which depletes the kinetic energy of the spinning magnet.

[CatalinaWOW]

Adding a question, what is the optimal size of a magnet that can be bolted to a 6000rpm motor for this? (I hope 1/2 or 1/4 wavelength can work...) What about one bolted to a 15000rpm SCSI hard drive spindle motor?

Guys on this forum are technicians, engineers and electronics hobbiests.  Shouldn't be afraid of numbers.  So do some calculating.

Go to a freshman physics book (perhaps yours) or google and find the centripetal acceleration involved with rotary motion.

a=v^2/r=w*r^2.  (Sorry, I am not a web guru or Latex maven and am not going to make the equations pretty.  Read w as omega, which is 2*pi*f).

You see that the acceleration goes as the square of the radius, and at a radius of 1/4 wavelength will be truly impressive. 

You need to do an integral to get the stress in the magnet, but some simple bounding expressions will tell you the neighborhood you are playing in.  Try assuming that all of the mass of the magnet is at half radius and at the full radius.   Or a couple of minutes of google will get you an exact (sort of) answer.   You can get the mass from the density and google will give you answers on the strength of materials.

This stuff takes minutes now in the age of the internet.  There is no excuse for not applying real numbers to simple problems like these. 

[T3sl4co1l]

then all you need to do is put the energy from the coil and place it into a motor that will spin the magnet. b00m, problem solved. take that facts and actuality.

kappa

You can do "/s" or an emote, instead of a Twitch meme.

Or you can use the classic memes,



Problem?

Tim

[T3sl4co1l]

I went to the woods and while harvesting mushrooms thought occurred: Antennas are impedance matched to "free space". This is what gets stuff out. Now for magnet to "slow down" it must also impedance match to something. Simple with loaded coil but what about original case of floating in "free space". Perhaps magnet should be subjected to some additional accelerations besides steady spinning to match with "free space"...

Well, what does impedance mean?

It's a ratio of voltage to current.

It's also a ratio of electric to magnetic fields (E in V/m divided by H in A/m is still ohms).  Hmm, that sounds useful!

We get magnetization directly off the magnet itself, so, wham, halfway there.

Where do we get volts?  Aha, from spinning it, Faraday's law!

So as you spin up the magnet, the impedance in its near field increases (from zero, when stationary -- no E, all H).  As it gets closer to electrical resonance, E/H approaches Zo, and radiation hits a maxima.

Tim

[MrW0lf]

Only small problem. Magnets spinning in free space are not known to slow down. Might even include some planets! Even worse, planets have more like grown and seemingly acquired energy
Of course experiment is king but in practice quite nightmare to set up:
- vacuum
- magnetic suspension with non-conducting magnets
- no conductors nearby
Fist couple of years would go into dealing with losses only

[RoGeorge]

It's important on what axis the magnet spins. If you spin it around N-S axis it won't generate radio waves, and it won't slow down by itself. Spinning it on an axis perpendicular to N-S it will generate radio waves, and will lose energy, so it will slow down.

The planets do slow down, at least the Earth is slowly slowing down for sure, that's what astronomers think.

[MrW0lf]

The planets do slow down, at least the Earth is slowly slowing down for sure, that's what astronomers think.

Some persons are even said to kill themselves because of depressing theories about heat death of universe, no need to take them too seriously.
As for spinning magnet case I will stick to opinion that we are missing some subtle details unless there is some experimental proof of contrary.
I will put this on todo experiments list with some modifications. Maybe someday...