I'm studying for the final classification of amateur radio licensing which is the Extra class and it's the hardest one. A lot of this test covers electrical engineering math and whatnot. Can someone tell me why reactance is measured with “j” as in -jX for capacitance and jX for inductance? Seems weird to have a variable as a final figure
Any electrical engineers here?
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the best way to study for the exams is just memorize the questions, just fyi.
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Why do they use complex numbers instead of just two numbers? Is there some special property of C they use that R^2 does not have somewhere?
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analog circuits and ac take a fair bit of math to fully analyze. If this were an EE course, you would have had 2 semesters of calculus based physics, 3 semesters at least of calculus and other math, plus classes and labs dealing with simpler circuits. You would probably only have one class that talks about this stuff unless you were doing analog circuits or power engineering as your major path.
If you didn't use complex numbers, the actual circuit analysis would be a nightmare by hand. If you were actually doing this as your job, you would be using circuit analysis software to simplify everything
This is officially the most ive thought about analog circuits like this since I took the class on them my junior year I think
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i2 = -1 and the rotations from that are important. As well as these rectangular coordinates, magnitude/angle polar coordinates are also used. So if you have a sinusoidal voltage of a given frequency it has voltage
. I considered polar coordinates the "native" form for voltage/current signals and rectangular coordinates the "native" form for component impedances. This allows you to use the same math as for DC circuits to figure out AC voltages and phases for a single frequency, and it turns out if you have multiple frequencies you can just add up all the results, keeping in mind that impedances are frequency-dependent.
Vand a phase (where the sine wave starts in the cycle) ofEx if you have a sinusoidal source across a 1 Henry inductor, you can use Ohm's law w/ the impedance:
and
V = IZ.Zfor an inductor isjLwhereLare real numbers, frequency and inductance. With this purely imaginary impedance you see multiplying theIbyjresults in aVwith a phase offset of 90 degrees.Jump in the discussion.
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Duh but you don't learn anything
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especially on the extra test, I find the only parts worth knowing are the regulations that are going to get you in potential trouble. Not to say it isn't all interesting or worth knowing, but the more technical stuff is probably stuff you would look up anyways even if you were an EE. I know I'm not dealing with analog circuits and AC very often. Kinda sad, all the guys I know that really know the analog side of things are past retirement age
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I literally have no stem background so all of this is very interesting and worthwhile to know for me. Tech and general were mostly boring but I took those like 10 years ago. The extra exam feels like an Electrical engineering into course
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hang in there lol. I think I had about 3 calculus classes and a year and a half of other classes before we touched on all that. I went the exact opposite direction with embedded low power systems, so i probably thought about ac power like 5 times in 4 years.
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