# How do you store AC?

by LightFantastic
Tags: store
 P: 41 How did Hertz do it with his spark gap transmitter?
 Sci Advisor PF Gold P: 2,515 hi there you don't need to store AC ... the power for the transmitter comes from a battery(s) why did you think that you had to ? have you read the wiki info on spark gap transmitters ? have a read of the link above and see if you still have questions cheers Dave
 P: 41 Http://youtu.be/NoeuVxYoNio?t=6m15s 6:21 he generates an alternating current which runs alomg these rods and acoss a gap... Dang you, Jim! Generates an alternating current? Talk about misleading... more like a temporary AC from a DC source
 Sci Advisor PF Gold P: 2,515 How do you store AC? there ya go :) what you may also not understand is that the spark itself is generating the AC current The spark isn't just a single pulse, but rather it is an oscillation of current back and forward across the gap ie AC and its that oscillating current that generates the radio waves that are emitted cheers Dave
P: 41
 Quote by LightFantastic Http://youtu.be/NoeuVxYoNio?t=6m15s 6:21 he generates an alternating current which runs alomg these rods and acoss a gap... Dang you, Jim! Generates an alternating current? Talk about misleading... more like a temporary AC from a DC source
Well I've never quoted myself before. Isn't this incorrect? Current in a DC battery never changes direction, therefore it is not AC in nature. Is there a better term for this?

Also,

If I tap the leads of a 9V, not only will current flow, but I will also get radiation. This radiation will seize to radiate when the current IS flowing.

Why?

Because once set in motion, the electrons can argue that they are at rest, and it is everything else that is moving.

Question

If I disconnect the leads from the 9V, I should get radiation again, correct?

How should I explain to someone the source of radiation? Movement of charge? I think that is misleading. How about when charge changes its state of motion?
PF Gold
P: 11,958
 Quote by LightFantastic Well I've never quoted myself before. Isn't this incorrect? Current in a DC battery never changes direction, therefore it is not AC in nature. Is there a better term for this? Also, If I tap the leads of a 9V, not only will current flow, but I will also get radiation. This radiation will seize to radiate when the current IS flowing. Why? Because once set in motion, the electrons can argue that they are at rest, and it is everything else that is moving. Question If I disconnect the leads from the 9V, I should get radiation again, correct? How should I explain to someone the source of radiation? Movement of charge? I think that is misleading. How about when charge changes its state of motion?
You will get a bigger spark when you disconnect than when you connected, in fact - so more RF energy on disconnection. Similarly, in 'Old' motor car ignition systems, the sparks were generated when the contact breaker was opened.
The reason you radiate RF power is because magnetic energy has been stored in the inductor and this energy is radiated because there is a LC circuit that resonates (by design) at the wanted Radio Frequency. Current flows back and forward around the resonant circuit until the energy has all been radiated away.

The example of a Spark Transmitter is not the best one to use to get an understanding of how RF power can be radiated. There are too many added complications, compared with a modern transmitter that uses an oscillator and amplifier.
P: 41
 Quote by sophiecentaur The example of a Spark Transmitter is not the best one to use to get an understanding of how RF power can be radiated
That is why I tried breaking it down to something so simple as shorting out a 9V. I see no reason for Hertz to use a gap in his transmitter to emit RF power. Can you not emit a photon without a spark? I believe it is possible to emit a photon without a spark. Suppose you were to short out the poles of a loudspeaker. Now take your hand, and move the diaphragm (cone) in and out. If you were to connect the leads from an oscilloscope to the terminals of a loudspeaker as the diaphragm was being pushed and pulled, you would see voltage fluctuating in a sinusoidal fashion on the oscilloscope. Current of course, would move in one direction, then in the other. It is my understanding that this very act will radiate RF power. The important thing to note here is that there is no spark involved.

And thus my confusion with Hertz and his gap. I see no reason for it.

Back to the battery. I do not know whether or not every atom within that length of conducting wire (the one shorting out the poles of a battery) are emitting photons or are all photons radiated from the spark itself.