# Need Help....

#### rrrr4950

Joined Dec 23, 2011
5
Can someone tell me which one is the correct Answer.
Which one of this correct equation?
Unable to figure out this question.

Impedance=Resistance+Inductance
Impedance=Resistance+Reactance
Reactance=Resistance+capacitance
Impedance=Capacitance+Reactance

Any help greatly appreciated....

Joined Dec 26, 2010
2,148
You cannot get direct answers to all your homework questions by posting them here. We are not allowed to do people's homework for them.

Answers to this kind of question can in any case be found by intelligent use of a search engine.

#### Ledwardz

Joined Oct 31, 2010
37
this guy could have told you the answer in a few minutes and summed it up better than any website or i ever could but instead he spent the time bitchin at you which annoys me slightly. What a way to encourage a new member into electronics..... so welcome to the forum.

anyways...... i have only being studying electronics for a year but from what i gather, impedance consists of a magnitude and a direction and is basically is a resistance that depends on a frequency. It is generally obtained by;

square root of (R^2 + jX^2) i.e. the hypotenuse of a right angle triangle where the resistance is a the adjacent and the reactance the opposite. The direction is tan^-1(X/R) if ya get wot a mean. so if i were to guess i would say that Impedance = Resistance + Reactance.

R is simply the resistance using ohms law and jX is the reactance (think of it as AC resistance for now and the j just tells us its an imaginary component)

in AC circuits the current constantly changes and the resistance which we are now calling the reactance for capacitance and inducatance is calculated using
Xc = 1 / 2*pi*f*C
Xl = 2*pi*f*L

for a much better explanation and to see how the reactances were derived check out this guy he sums it up in 15 mins. It's well worth the watch and sorry i couldn't help anymore.

#### MrChips

Joined Oct 2, 2009
20,916
When will posters learn "Need Help..." is a useless title for a post?

#### MrChips

Joined Oct 2, 2009
20,916
this guy could have told you the answer in a few minutes and summed it up better than any website or i ever could but instead he spent the time bitchin at you which annoys me slightly. What a way to encourage a new member into electronics..... so welcome to the forum.
If posters are not told, how are they supposed to know they are doing something wrong?

Firstly, they should look at some posts and learn proper etiquette. It helps nobody to post "Need Help". Everybody needs help.

Secondly, they must be told that Homework will not be done for them.

Thirdly, anyone asking for urgent answers will get an answer a bit later.

#### Ledwardz

Joined Oct 31, 2010
37
If posters are not told, how are they supposed to know they are doing something wrong?

Firstly, they should look at some posts and learn proper etiquette. It helps nobody to post "Need Help". Everybody needs help.

Secondly, they must be told that Homework will not be done for them.

Thirdly, anyone asking for urgent answers will get an answer a bit later.
all you have to do is point him in the right direction, not give him the answer. Hey kid maybe you could change the title to something relevant and show us what you already know would suffice.

#### rrrr4950

Joined Dec 23, 2011
5
Just wanted to thank you Ledwardz very much for your help.
Thank you for your support regarding Senior Member comment greatly appreciated. Im new to this forum. Way to encourage new member I thought this is friendly blog forum. If it inconvenient for you to answer the question. Please dont waste your time just disregard the question and move on.

#### justtrying

Joined Mar 9, 2011
429
Just wanted to thank you Ledwardz very much for your help.
Thank you for your support regarding Senior Member comment greatly appreciated. Im new to this forum. Way to encourage new member I thought this is friendly blog forum. If it inconvenient for you to answer the question. Please dont waste your time just disregard the question and move on.
It is too bad about your experience, but you were actually encouraged but in a rough way

1. use a descriptive title
2. do not just post a question but an attempt at solution or a description of why you find it confusing (this shows you have thought about it)

these two steps work every time. You will get help. It may not be prompt, depends on who is on line.

#### MrChips

Joined Oct 2, 2009
20,916
If the op had taken the time to Google "impedance" or "reactance" he would have gotten the answer immediately.

#### thatoneguy

Joined Feb 19, 2009
6,359
Before complaining about those of us who volunteer freely to help, please do us a favor and read the sticky about "HOW TO POST QUESTIONS IN THE HOMEWORK FORUM".

Then there would be no misunderstandings, and no disgruntled people.

Too many people make one question an image to paste onto a bunch of sites, looking for an answer as soon as possible (not in this case, but it is extremely common). If that time was spent writing the question correctly, it would be answered, usually within an hour or less for a question like this, on this site alone, saving a lot of time for all involved.

#### rrrr4950

Joined Dec 23, 2011
5
I dont have any misunderstanding or not disgruntle person.
Just wanted get wanted my pass my exam. Is that a problem.

#### spider87

Joined Dec 9, 2011
7
I dont have any misunderstanding or not disgruntle person.
Just wanted get wanted my pass my exam. Is that a problem.

Yes because you should not pass an exam if YOU don't know the information that is on it. The exams are there to gauge YOUR knowledge of the subject NOT the forum's knowledge of it.

Not to mention that a simple google query would have answered this for you!

#### thatoneguy

Joined Feb 19, 2009
6,359
Yes because you should not pass an exam if YOU don't know the information that is on it. The exams are there to gauge YOUR knowledge of the subject NOT the forum's knowledge of it.

Not to mention that a simple google query would have answered this for you!
Yes, Google could have told him the answer just as easily as we could have.

Understanding WHY that is the correct answer is where learning takes place, otherwise it's just rote memorization that can't be applied well.

#### spider87

Joined Dec 9, 2011
7
Yes, Google could have told him the answer just as easily as we could have.

Understanding WHY that is the correct answer is where learning takes place, otherwise it's just rote memorization that can't be applied well.
It's important that a student knows how to find the answer on their own as well. Someone won't always be around for you to ask.

I'm not sure how you took my comment but my point was NOT centered on the google portion of it. That was simply an addition. The important part is that the exam is to test the student's knowledge. Whether it be rote memorization or not, it is important for the student to know it OR know where to find it on his/her own.

#### thatoneguy

Joined Feb 19, 2009
6,359
I'm not sure how you took my comment but my point was NOT centered on the google portion of it. That was simply an addition. The important part is that the exam is to test the student's knowledge. Whether it be rote memorization or not, it is important for the student to know it OR know where to find it on his/her own.
I'm guessing he had no clue where to start, and the information in Post #3 cleared that up.

The only reason I am making any sort of issue about it is that information is as intrinsic to electronics as Ohm's law, and if he doesn't understand it fully and quickly, he'll be out of the loop entirely.

#### MrChips

Joined Oct 2, 2009
20,916
Just wanted get wanted my pass my exam. Is that a problem.
I think we all recognize the problem and are saying the same thing. Anyone in an electronics course should not be asking a question like this one. It's like asking "What is Ohm's Law useful for?"

Joined Dec 26, 2010
2,148
this guy could have told you the answer in a few minutes and summed it up better than any website or i ever could but instead he spent the time bitchin at you which annoys me slightly. What a way to encourage a new member into electronics..... so welcome to the forum.

anyways...... i have only being studying electronics for a year but from what i gather, impedance consists of a magnitude and a direction and is basically is a resistance that depends on a frequency. It is generally obtained by;

square root of (R^2 + jX^2) i.e. the hypotenuse of a right angle triangle where the resistance is a the adjacent and the reactance the opposite. The direction is tan^-1(X/R) if ya get wot a mean. so if i were to guess i would say that Impedance = Resistance + Reactance.

R is simply the resistance using ohms law and jX is the reactance (think of it as AC resistance for now and the j just tells us its an imaginary component)

in AC circuits the current constantly changes and the resistance which we are now calling the reactance for capacitance and inducatance is calculated using
Xc = 1 / 2*pi*f*C
Xl = 2*pi*f*L

for a much better explanation and to see how the reactances were derived check out this guy he sums it up in 15 mins. It's well worth the watch and sorry i couldn't help anymore.

I'm a bit at a loss here. I answered this poster' s first "need help" question directly, somewhat against my better judgement (and, I suspect, not really in line with forum rules). This is the thread:http://forum.allaboutcircuits.com/showthread.php?t=64235

Faced with a second query on facts which could easily be found from a web search, I decided not to answer, as it looked as if the OP was simply reeling off the questions on his assignment one by one.

Perhaps I should simply have ignored both of these questions?

#### JoeJester

Joined Apr 26, 2005
4,259
Just wanted get wanted my pass my exam. Is that a problem.
One of the recommendations in the "How to post in the Homework" rules was the OP should show their attempt at answering the question.

For this OP, it would have been simply, analyzing each answer and try to eliminate them from being the correct answer. That would have showed the members here you are making an attempt and where you went astray.

Of course that wasn't done.

As much as we urge people not to connect circuits directly to the mains ... the one video certainly projected a disregard to safety, although they did mention safety at one point in the video.

#### Ledwardz

Joined Oct 31, 2010
37
I'm a bit at a loss here. I answered this poster' s first "need help" question directly, somewhat against my better judgement (and, I suspect, not really in line with forum rules). This is the thread:http://forum.allaboutcircuits.com/showthread.php?t=64235

Faced with a second query on facts which could easily be found from a web search, I decided not to answer, as it looked as if the OP was simply reeling off the questions on his assignment one by one.

Perhaps I should simply have ignored both of these questions?
sorry. hadn't seen then other post.