is "in" and "out" negative or positive ? SOLVED

i'm not familiar with electronics and i'm very confused as to to the values of "in" "out" and "to ground" and how on schematic diagrams a positive and negative input can seem to have a single wire output.

by freggeth
January 07, 2021

1 Answer

Answer by ConnorBecz

It would help if you could show an example of the type of circuit you are referring to, but basically, positive and negative voltages refer to the amount of potential energy at different points in a circuit. Positive means a surplus of electrons that need to flow somewhere. Negative means a DEFICIT of electrons and is an interesting case where this region of the circuit is going to suck up electrons until the holes in their atomic shells are full.

Ground is what they call any path or point in the circuit/device that rests at 0 potential energy. Neither any holes nor surplus electrons. Ground draws electrons towards itself with the promise of a reservoir into which the extra electrons will flow and come to rest at long last. Negative voltages ALSO draw electrons, trying to fill the holes. Therefore, positive voltages are drawn toward ground, but they are drawn MORE strongly to negative voltages.

Now, what I'm trying to lead up to here is, you can have just one wire which carries the output of a circuit no problem. The output probably flows into a different mesh. As long as there is either a point of ground over there, or a point of negative voltage, electrons will be drawn out the single-wire output and off into the other part of the circuit. They don't need to return to the voltage source through any kind of designated negative path. They can just flow to the next ground point, or to anywhere where there is negative voltage.

I'm not sure what you mean by negative input, but assuming you're referring to an AC signal?

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by ConnorBecz
January 07, 2021

thanks, is the output of an op- amp positive or negative ?

by freggeth
January 07, 2021

It's often negative, as in the case of a common-emitter amplifier. However, whether a voltage (or current, for that matter) is positive or negative typically depends on whether or not you are using the positive reference direction to analyze the circuit.

If you analyze a circuit with the assumption that current is flowing one way, but in reality it is flowing the opposite way, then what you will discover mathematically is that the current appears to have a negative value. You may calculate that the voltage of a source or an element is negative too, if you analyze a circuit this way. To be blunt, it's just because the flow of current is actually backwards of what your model is saying it should be.

For these reasons, you can have a negative output from an op-amp, as is not uncommonly the case, but it just means that the current is actually flowing opposite of the direction implied by the circuit schematic.

by ConnorBecz
January 08, 2021

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