Questions about RLC circuits and OP amps

[slain4ever]

Hi guys I really need some help to finish this on time,

1. A circuit with V volts and a 2 ohm resistor and a 2mH inductor and a 500uF capacitor in series.
There is a graph of current through circuit over time, starting at 0 current icnreases to 20 amps in 1 mS stays there for 1 ms then goes down to -20amps in 2 ms stays there for 1ms etc.

I need to sketch the voltage across the resistor and across the inductor


2.
a RLC series circuit, R=500 ohms, L=0.4 mH and C=100pF, connected to AC source with a RMS voltage of 1V and variable frequency

calculate a) the resonant frequency, b) the inductive and capacitive reactance at resonance, c) the impedance at resnance d) the RMS current at resonance e) the RMS voltage across each element at resonance.


any help would be greatly appreciated as i am very lost

 

[ideasrule]

Do you have any idea where to start on any of the questions? If not, I think you need to review your textbook's chapter on electrical circuits. That would be much more helpful, and probably less time-consuming, than me trying to summarize all the material for you.

 

[slain4ever]

ive got some ideas, just can't remember which formulas, just show how to work it out and ill understand, like step by step

 

[slain4ever]

ok so i think I've pretty much got it,

but some thigns I am stuck on is in the first question (1a.) do you use the resistance of the resistor to graph it? ie 2 ohms or do you use z (impedance i think its called) (which turns out to be 2.01 ohms.

so for 1a I've got the graph currently the same as the current-time graph as a voltage time graph with max value of 40.17, not sure if it should be 40, and I am pretty sure it should be in phase.
with b I am almost certain that it should go to 40.17 but be off phase by a quarter, so shifted 1.5ms to the right.

Question 2 I am having some trouble with d
with d the equation is (i think) i=v/r my problem is what is the value of v? do i leave it in rms? or convert to peak or peak to peak or what? using a simulator i got 4mA which is 1*2/500 which appears to be peak to peak rms?? which makes no sense to me

 

[slain4ever]

any help?

 

[Mindscrape]

What!? These questions have nothing to do with op amps. I love op amps and that's why I came to look at the topic, grr. Fine, I'll give you a kickstart even though I'm disgruntled.

1) Phasors are your friends. If you don't know them, well you should have shown more work and more of the problem.

2)
a) You can either derive this or look it up in your book (probably even wikipedia)
b) Same as a.
c) Once you know the resonance frequency you can plug and chug with the ZC and ZL.
d) Look up RMS/Ohm's Law and use it, again phasors are your friends.
e) Same as d.

The easiest thing to do is learn MATLAB (there's open source versions) and have it do whatever grunt work you need.