impedance vs. resistance

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Designer69

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I will say that I don't have a solid understanding of the difference between inpedance and resistance. can someone help with a link to some good reading material or something?

thanks
 
Impedance includes inductive reactance and capacitive reactance, and is more commonly considered with AC circuits. Sorry, I don't have any references offhand, but an internet search should turn up tons of material. Any basic AC circuits textbook should also explain it.
 
One way of looking at wave forms__- think of a normal sine wave ... imagine a car wheeltravling up and down this bumpy road.. resistance is like the power needed to propel the vehicle.
inductance is like a spring, coiling and uncoiling ....., and capacitance is like a shock absorber evening out the bumps.
This analogy may be more suited to DC circuits rather than AC circuits. If you look at oscilloscope waveforms of a simple 110 AC to 12Vdc battey charger it will make sense. While charging, the battery provides simple resistance, A diode bridge will provide a doublesine waveform, then add a capacitor, and the sinewave will level out to a flat DC voltage line.

Find a college levelbook on AC/DC circuits and try not to read very fast or think too much. It gives me headaches and has no real info on how to make a buck.

I have made a lot of money slinging wire and trouble shooting residential and industrial equipment, as opposed to my B.S. degree in electronics.
The electroinics end is more intriguing, but not very employable in this neck of the woods.
 
rt66electric said:
This analogy may be more suited to DC circuits rather than AC circuits.
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I kinda like the analogy. One could thing of DC, or non-reactive AC, as the straight-line motion of the car, and the reactive power as the additional distance the wheels themselves must actually travel, including the ups and downs.



Or not. :cool:
 
Designer69 said:
I will say that I don't have a solid understanding of the difference between inpedance and resistance. can someone help with a link to some good reading material or something?

thanks
Click to expand...

"Resistance" refers to load that isn't related to time. That means if the voltage increases, the current increases directly in proportion to the voltage - double the voltage, double the current. Doesn't matter how fast or slow the voltage is changed - the current changes just as fast or slow. "Impedance" refers to a load that has a time related aspect to it (the reactive part of the load). It takes into account how the the current changes over time when the voltage changes over time. For example, with an impedance that describes a reactive load, if you double the voltage over time, the current might either more than double (capacitance), or less than double (inductance) over that same period of time. This is the difference between algebra (resistance) and calculus (impedance). The actual term "impedance" is typically used with a simplified mathematics that has developed specifically to deal with systems of sinusoidal voltages - much easier than resorting to the basics of calculus to figure out how an AC circuit behaves!
 
LarryFine said:
But, isn't the "time" we're talking about really sub-cycle time, and not over many cycles?
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Well, for the actual underlying calculus, the "time" is an infinitely small period called delta-T ("dT"). But in simplifying the math for use in AC sinusoidal systems, the time domain equations are transformed into frequency domain equations. While with this transformation we lose the ability to handle arbitrary waveforms, we greatly simplify the analysis of AC sinusoidal systems. So ultimately we don't see "time" in the equations used for analyzing impedance in AC systems - we see frequency.
 
jumper said:
If you really want to understand and calculate it, you are going to have to learn a "new" math.
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I did not know Trigonometry was New Math. Heck when I took it we used Slide Rules, we did not have calculators or computers back then. You actually had to understand what you were doing :)
 
dereckbc said:
I did not know Trigonometry was New Math. Heck when I took it we used Slide Rules, we did not have calculators or computers back then. You actually had to understand what you were doing :)
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I never took a regular trig class in high school, so I am not sure of what they teach. So later when I went to college and learned about complex numbers and the j(i) operator it was new to me.

The idea of the square root of -1 was hard for me understand the first time I saw it.
 
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