Induced Voltage?

[donbenjy]

hey, i wa just thinkin about the really basic fundamental physics of a guitar...obviously the magnets and coil create a magnetic field above the guitar, to the strings, and then when a string moves, it causes induced voltage, but i was wondering, does the 1.5V in the jack flow constantly and then the amp/pedal/DI box/mixer etc pick up those changes and then turn them into sound waves? also, on induced voltage, does anyone actually know why moving a wire in a magnetic field can cause this, even when not attached to a power supply? my physics teacher (who teaches A level) cant explain it 2 me, im sure lovekraft will know if noone else i just dont get how copper wire can be charged by magnets when its not a magnetic material?!?

[lovekraft]

No, there is no static DC voltage coming from your guitar - the pickups are at ground potential until the string moves. It's exactly like an alternator - no movement = no voltage. The string "moves" the magnetic field, and as the field "moves" across the pickup coils, it generates an alternating current in exactly the same way an alternator does. Is that helpful, or am I muddying things up further?

[donbenjy]

hehe no, that maks sense so the 1.5V in the jack, is that only used to power the components inside? or does that just run straight to ground?

lol sorry,how does an alternator work?

[lovekraft]

Most guitars don't have 1.5 volts DC anywhere - I'm not sure where you got that figure.

For an explanation of how generators/alternators/dynamos work, try these links:

http://science.howstuffworks.com/electricity3.htm

http://www.bbc.co.uk/schools/gcsebitesize/...ctionrev3.shtml

http://en.wikipedia.org/wiki/Electromagnetic_induction

http://en.wikipedia.org/wiki/Electrical_generator

http://www.slcc.edu/schools/hum_sci/physic...0/em_induction/

If that doesn't clear it up, ask your physics instructor to eplain the parts you didn't understand. Sorry, but I'm rubbish at trying to explain the basic stuff with magnets and wires. All that stuff about lines of field, flux and Michael Faraday... yecchh!!

[donbenjy]

lol the jack plug? isn't that 1.5v? or does that mean maximum voltage? hmm maybe i read somethin wrong somewhere? but then, does that mean if you had a big enough tranducer, you could plug a guitar into a speaker, unpowered and get some sort of sound? even if it was small?

oook, my physics teacher actually CANt explain exactly why it induces voltage, im only 16, our course only requires that we take it as read that moving a wire through a field induces voltage/current, was just wondering, on a molecular level why this would happen?

[lovekraft]

Yes, theoretically if the string had sufficient mass, the magnets and coil were large enough and the speaker was sufficiently sensitive, you could get it to vibrate without any amplification.

I suppose that some really hot pickups might reach 1.5vac P-P, but that's unusual.

As for the molecular explanation of electromagnetic induction, see if this helps:

http://www.ux1.eiu.edu/~cfadd/1160/Ch21Ind/Cond.html

It uses some fairly advanced equations, but the pictures may give you an idea - beyond that, it's Google time. Like I said, I'm rubbish at that part, I simply accept that it does.

[daveq]

That's funny - I remember doing a presentation (more like show and tell) in 6th grade on how electric current can be generated by a wire and magnet. I was really into those race car sets back then - the ones with the two power rails and a center groove to help keep the cars on the track.

I think if you just dump the 1.5V thought completely, that might help. Just forget it was ever in your head.

In a very basic system, the signal created by the strings moving in the magnetic field gets amplified and sent to a speaker. The speaker cone moves (again with the help of magnets and wires) in synch with the signal and moves the air. The movement of the air is what ends up creating the sound. It's more complicated of course but that's a simple description.

Try to think of it as the magnetic field forcing electrons in the wire to move. The movement of the electrons (electronics guru's will complain about hole vs. electron movement but lets not go there) is what ends up creating the current / voltage. It's like converting one force into another. Kinetic energy being converted into electrical energy.

Maybe that's just confusing but in my twisted mind, it makes sense.

[donbenjy]

hmm i think i get it!!! the electrons are affected by the field and travel up/down the wire to incude a flow of electricity!? lol 6th grade? is that like when you weer 10 or 11? lol the part of electromagnetism we're studyin is aparently the hardest part of the whole course!!!