How do passive circuits work with no battery/power source?
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One example might be the volume and tone controls on an electric guitar.
You don’t turn up the volume or the tone (treble frequencies), you turn down the amount which is lost to ground.
Passive circuits are generally components in a larger system, they have power flowing into them from somewhere else.
For example, in a passive low pass filter the power is coming from the input signal, and some of it is dissipated by the filter. The power of the output signal decreases as the frequency increases, but is never more than the power of the input signal.
Some radio receivers can operate without a power source since the radio waves hitting the antenna can induce some, albeit very little, current (E.g. [the foxhole radio](https://en.wikipedia.org/wiki/Foxhole_radio?wprov=sfla1)). I would imagine that the same concept might be applied in some modern devices.
All circuits have a power source of some kind. Passive means it does not input any power into the circuit but can still modify things with the power that was provided.
Active circuits can provide power to the circuit.
The volume example is great. It provides resistance and changes the output but adds nothing.
An active circuit needs power outside of it’s input signal to perform. Passive just needs the input signal.
Another definition is that all passive circuits are made of integral, linear, or derivitive transforms of their inputs, while active has non-linearity.
Power source is the part that’s probably the vaguest and most complicated. If you mean electrical supply then you have passive radio receivers or near field circuits which get their power from radio waves and bounce back a code with the power given to thwm by the radio waves.
There is no circuit (that i can think of) that has no form of power coming in. The power isn’t always direct electric current
A passive circuit is generally made up of resistors, capacitors and inductors. Thr equivalent to these are water tubes of varying widths(resistor), overflow tanks(capacitor), and long pieces of tube(inductors). The water still has to flow though it for the circuit to do something.
I think you’re possibly misunderstanding the term “passive” in the context of electrical components. Let’s take a capacitor, as an example. A capacitor is considered a passive electrical component. You apply a charge to it, and the capacitor will “store” the charge. The power source is external to the capacitor, but there is still a power source.
The opposite of a passive component is an active component. Active components either provide the source of power (like a battery) or control the flow of current (like a transistor).
There is quite a bit more to it than this, but that’s probably a good ELI5 level answer. If you want more detail, Tutorials Point actually has a good page on the subject: [Difference between Active and Passive Components (in Electronics)](https://www.tutorialspoint.com/difference-between-active-and-passive-components-in-electronics)
Through stelling power power in an existing system as a add on that wasnt intended, plunging into a system by design, or through beeming with say the case of Antennas or (If I recall) toll cards and more commonly chips in bank cards.
Well it has to be a component that uses Faraday’s law to drive the circuit.
Many examples in everyday life al the way from RFID energy harvesting to galvanic isolation. Both use the same principle. Even transformers.
It doesn’t even have to be Faraday’s law. A photo diode is another example. But this is the only example I can think of that doesn’t use Faraday’s law. Even hand cranked devices is an example of faradays law.
I guess the answer is Faraday’s law. You may find only exceptions like a photo diode or say a solar panel.
Even power plants use the same principle as a store bought hand-cranked torchlight.
Edit: I just saw the other comments, idk why so many people are providing definitions and examples of what a passive and active circuits are. That’s not what the post is asking.
It’s very simple. A passive circuit cannot work without a power source. That’s in the definition.
By extention, you have two components in impedance and power: real and reactive. The reactive component is the imaginary part that capacitors and inductors produce. The real, unreactive components are resistors. Technically everything produces heat losses and has some resistance.
The real part is the part that produces heat losses. The reactive or imaginary, part produces losses by way of phase changes and depending on the application, bouncing back energy. Imaginary power is a very intriguing concept.
To get an accurate idea always convert everything into polar form.
I mentioned this because not all passive components theoretically produce heat losses, but practically do. But again, depending on the application, heat losses aren’t the only type of losses.
Edit: at the end of the day, a passive component does some work, that it’s designed to do.
Something to keep in mind is engineering is very purpose driven.
Edit:
Maybe you can think of passive circuits as ones “waiting” to receive power.
When you cover Thevenin’s theorm or start Signals and systems it should become clearer.
When you cover thevenin’s theory, you’ll learn to look at a circuit as a black box.
When you cover Signals and Systems, you’ll learn to look at a circuit as a Transfer Function. In a way, a mathematical extension of the same concept.
Edit: some of these comments are scary. Hope they’re not practicing engineers. Holy fuck its scary.
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