Eddy Current
Senior Member
Does a sine wave go up and down or is it like a coil going round and round? If you look on the wiki page for sine wave there is a gif that illustrates a sing wave. Is that true for all sine waves including electrical ones?
An electrical sine wave in 3D
- Thread starter Eddy Current
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A sine wave (sinusoidal waveform) just goes up and down. The "trace" appears the same as looking at a 3D spiral from the side.
eHunter
Senior Member
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- North Texas & Georgia
Both. A sine wave is three dimensional. It is usually graphically represented as a two dimensional rising and falling line moving accross a time axis. This is usually repesented two dimensionally as:
This is closer to a three dimensional representation.
I disagree. In three-dimensions, it is a spiral, not a sinusoidal waveform.
eHunter
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- North Texas & Georgia
How do you propose to generate a spiral without a sine wave?
Mathematically a spiral is a sine wave.
A sine wave could be considered a planar component of a spiral... but the sine wave is not necessary to construct a spiral. A spiral marks the off-axis end of a rotating radial moving along an axis at a constant rate.
A sine wave doesn't actually exist in a spiral... it is only a sideways projection of the spiral onto a single plane. In the animated image you embedded, note the sine wave only exists on the X-t plane. Any "Y-axis" magnitude of the spiral is imaginary with respect to the sine wave itself.
What did you do to your avatar? It moves like it is supercharged now..
Nothing.
Did you change or update your browser? I don't know why, but different browsers display it at a different speed.
A sine wave voltage has two components. Voltage and time.
A pendulum swings with SHM in two dimensions.
I fail to see how a sine wave is three dimensional since voltage and current do not spiral, rather they stop and start with increasing and decreasing amplitude. There is a definite zero point, and in a helix there is no zero point, what you have in the .gif is a helix.
jumper
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al hildenbrand
Senior Member
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- Minnesota
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- Electrical Contractor, Electrical Consultant, Electrical Engineer
Part of the brainteaser in this, I think, comes from most of us using electrical objects that are three dimensional.
Marrying in one's mind, the theoretical concepts to electricity, almost always represented in two-dimensional space, with the real world 3D assemblies we make, affords the cognitive dissonance.
Consider an energized wire connected to, and delivering current into, the center of a large flat buss bar. The current and voltage "waves", propagating at near light speed are like the ripples on still water. . .
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weressl
Esteemed Member
Nope a spiral never changes its value, just its position in the three dimensional world. A sine wave never HOLDS the same value, it constantly changes.
hurk27
Senior Member
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- Portage, Indiana NEC: 2008
I have to agree with Al, the waves of an AC voltage can be a spiral if the material it is passing through is large enough for the wavelength size, we only reference the wave from a small point that we can only see the sign wave as the wave pass by this single reference point, for a true 3-D image we would be looking at a spiral ball, think of an explosion under water, the shock waves would radiate out from the explosion point in all directions, just like radio waves do in the air when a plane transmits, the sign wave we use to represent AC is just the stationary single point of reference of the wave propagating out from its source, just because we tend to only take measurements from a wire, the sign wave we see is only relative to that point where we took our measurement, if we had a conductor that extended out in all directions from the source we would see this spiral ball radiating out from this source point, while the wave hight of a sign wave is relative to the voltage creating it, and the spacing of the waves is relative to the frequency of the voltage, don't confuse the wave hight with the wave length, as wave length is the distance between each wave in a sign wave as it is in a spiral wave hight is relative to the pressure of the wave or voltage, the 4th dimension is the speed at which the wave travels which is what really give us the frequency as if you were to move your measurement point down the wire at half the speed of light then the frequency would be half the 60hz or 30hz, this is why everything is only relative to the point at which we take our measurement, but if we could see the movements of the wave like we can with kinetic energy in water, we would see that same spiral that one would see in water.
weressl
Esteemed Member
The sine wave is "created" by the rise and fall of the potential over time, it does not exist as a distinct physical shape and it has absolutely no relationship to the 'movement' of electrons or other particles.
hurk27
Senior Member
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- Portage, Indiana NEC: 2008
Actually I don't see AC current as a spiral but equally spaced rings of waves traveling out from the source at the speed of light, I didn't catch this until I re-read my post, it is not a continuous line of a single wave spiraling out, but separate closed wave circles or balls in a 3-D view expanding out from the center at the speed of light, this is the same thing you see when you drop a marble into a body of water, the waves do not form a spiral, just rings of waves and continue as long as there is a source to produce them.
You may ask then why do we see many of these waves after only dropping one marble, its call resonate, or the water that keep resonating after the energy has stopped, just like when a guitar string is plucked, or a piece of metal is struck, we see the same thing with inductance, but the hight of the wave or voltage drops off fairly fast.
You may ask then why do we see many of these waves after only dropping one marble, its call resonate, or the water that keep resonating after the energy has stopped, just like when a guitar string is plucked, or a piece of metal is struck, we see the same thing with inductance, but the hight of the wave or voltage drops off fairly fast.
al hildenbrand
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- Minnesota
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- Electrical Contractor, Electrical Consultant, Electrical Engineer
Theoretically . . . yes.
But then there is the movement of the mass of my Sawzall blade relative to time.
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Electromagnetic waves move that way. But current is a more localized phenomenon, tied to actual movement of charge carrying particles (except for displacement current, as in a capacitor, and we will ignore that....)
And in the case of electromagnetic waves, the electric and magnetic field components exist in three dimensions and you can, in the case of circularly polarized light, look at it as a moving and rotating electric field vector. In that case, the projection of the vector in any plane parallel to the direction of travel of the wave will be a sine wave function of time.
But voltage and current just do not work that way; voltage is a scalar field, not a vector field like the electric or magnetic fields. The representation of current in the vector form a + bj is just a way of allowing for a displacement in time from a reference waveform and does not have anything to do with two or three dimensional physical space.
Current, on the other hand, does have both a magnitude and a direction, although we can consider a single wire as a one-dimensional current path for some purposes.
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