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I got confused when I encountered this problem on Chegg.

https://www.chegg.com/homework-help/questions-and-answers/5-find-ac-current-source-iin-polar-form-b-find-vt--c-choose-one-source-current-leads-sourc-q19121964

Question: 5.

a) Find the AC current source, Iin in polar form.

b) Find VT .

c) Choose one:

i) The source current leads the source voltage.

ii) The source current lags the source voltage.

enter image description here

My question isn't about solving the problem. Do AC current sources exist? I've tried searching and they don't pop up except for the Chegg problem I saw. I also recently took a Circuits class and three basic active components discussed to us are the DC voltage source, AC voltage source and DC current source. I don't get if they exist at all, and if so why is information about it not as common?

EDIT: People might answer only about the actual AC current source. I am also talking about theoretical. Like can I do the same thing in Chegg where you put a wave symbol and an arrow and call it a theoretical AC current source? How would you then use it in computations? Do you just attach a phasor to it and use current in the x-axis instead of voltage for vector diagrams?

It's because I'm curious on both. Yes I want to know whether they exist in real life but I also want to know their "existence" on our theoretical computations. Are they there but scarcely used? Or do they not exist at all on common electrical circuit related courses?

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    \$\begingroup\$ Perfect voltage and current sources DO NOT exist. So, if you are prepared to accept an imperfect source then sure, they can be made and that means they exist. \$\endgroup\$
    – Andy aka
    Jan 17 '21 at 13:40
  • \$\begingroup\$ Would you consider a current transformer as an AC current source (within certain bounds)? \$\endgroup\$
    – Transistor
    Jan 17 '21 at 22:07
  • \$\begingroup\$ For actual, I guess. But for theoretical, I was wondering if there is a certain symbol or concept that is actually made for an AC current source and not "this works like that so it counts" since we are talking about theoretical anyway. \$\endgroup\$
    – AndroidV11
    Jan 17 '21 at 23:25
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Ideal AC and DC voltage and current sources are useful for analysis (theoretical) purposes.

It could be said that an AC generator that supplies power to a grid operates as an AC current source. There are also AC motor controllers that act as current sources. However it may be more accurate to say that they are DC current sources that control motors through inverters. That is a DC current source drives an inverter that supplies current to a motor. Grid connected solar and wind power inverters are similar.

Re edit:

Like can I do the same thing in Chegg where you put a wave symbol and an arrow and call it a theoretical AC current source? How would you then use it in computations? Do you just attach a phasor to it and use current in the x-axis instead of voltage for vector diagrams?

Yes

Re Comment:

Here is an example from Scott, Linear Circuits, 1960. It clearly shows an AC current source, but the symbol doesn't include as sin wave symbol. I also found textbook problems that simply identified the source i(t). Some of those were sine wave sources and others defined some other periodic waveform. enter image description here

Also note that a current transformer act as a current source.

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  • \$\begingroup\$ Just want to ask, are you aware of other references that show an AC current symbol that has a wave and arrow? I'm just really curious because why don't they teach something like that commonly when it's a theoretical anyway? \$\endgroup\$
    – AndroidV11
    Jan 17 '21 at 23:27
  • \$\begingroup\$ See addition to answer. \$\endgroup\$ Jan 18 '21 at 0:33
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An AC generator with a very high output impedance can be approximated as a current source...as long as the range within which the load impedance is significantly smaller than the aformentioned output impedance.

Example: If you have two resistors connected across a voltage source and and one is 1MOhm (we will call this the output impedance) and the other only ever varies between 0 and 1000Ohms, the current is going to be essentially the same because the resistance of the circuit essentially doesn't change since it is dominated by the 1MOhm.

This is why in differential long-tailed circuits you sometimes see current sources but other times you see resistors.

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Yes AC current sources do exist, my favorite is: Keithley 6221 Low Noise Precision AC/DC Current Source with GPIB and RS232 Interfaces. I know this answers your question but not your problem.

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