Hi I’ve got this question. Doing RLC series circuit. I’ve got a formula sheet that says for capacitor reactance I use formula xc=10^6/2pieFC) when capacitance is in microfarads. The problem I have is the working out in the answers is a different formula and I have no idea where they get 6.28 from? Can someone please explain why I cant use the formula I’m using and what I should do. View attachment IMG_9074.jpegView attachment IMG_9069.jpegView attachment IMG_9072.jpeg

 

Errr 6.28 is 2π to 2 DP.

Your formula is exactly the same,but for μF rather than Farads

The difference in results is they've used 6.28 rather than the PI key....


You need to stop, take a deep breath and just think it through a while...

 

\( 2\pi\;=\;6.283185307... \)

\( X_C\;=\;\cfrac{1}{2\pi fC_F},\text{ Capacitance in farads, frequency in Hz.} \)

\( X_C\;=\;\cfrac{1\times\;10^6}{2\pi fC_{\mu F}}, \text{ Capacitance in }\mu\text{Farads, frequency in Hz.} \)

 

BTW, welcome to AAC

 

Errr 6.28 is 2π to 2 DP.

Your formula is exactly the same,but for μF rather than Farads

Ok. Thanks I get 6.28 is the formula. But how is my formula the same? In my working I got 795.77 ohms and their working out they got 796.17ohms?

 

BTW, welcome to AAC

Thankyou! I’m an electrical apprentice (can probably tell by user name) and trying to wrap my head around all this. Appreciate your replies. Thanks

 

Ok. Thanks I get 6.28 is the formula. But how is my formula the same? In my working I got 795.77 ohms and their working out they got 796.17ohms?

So let's look at the difference between what you got and what they got.

The difference is 0.4 Ω. which is just 0.05%

Now consider the difference between 6.28 and 2π, which carried out a few more places is 6.28319. That a difference of 0.00319, which is 0.05%.

So the difference is due to the difference in the estimate of π that was used.

Another way of looking at it is that 6.28 is 2π represented to 3 significant figures. That means that your answer is only going to be good to, at best, three significant figures. So round both answers to three sig figs and, in both cases, you get 796 Ω.

 

Don’t tell me to stop or take a breath buddy. Im just trying to understand the question. Nothing wrong with that. By the looks of thing you need to take a breath more than me..

You came here asking for free help from strangers. If you are unappreciative when those strangers take the time out of their lives to provide that free help, then don't be surprised when they, and everyone else seeing your response, elect to spend their time elsewhere instead of providing free help to someone that isn't going to appreciate it.

 

You came here asking for free help from strangers. If you are unappreciative when those strangers take the time out of their lives to provide that free help, then don't be surprised when they, and everyone else seeing your response, elect to spend their time elsewhere instead of providing free help to someone that isn't going to appreciate it.

If you want to answer for someone else then you are more than welcome.but before you go calling me unappreciative go up and read earlier in the thread. I literally said thankyou and that I did appreciate your replies.

 

If you want to answer for someone else then you are more than welcome.but before you go calling me unappreciative go up and read earlier in the thread. I literally said thankyou and that I did appreciate your replies.

And I couldn’t care less who replies. Delete your reply to my question and move on!

 

OK, I don't normally reply to those that leap down my throat, but in my view of your question you seemed to be panicking, so I gave you the same advice I'd give any of my students. Maybe it wasn't obvious to you, but putting the two formulae side by side it should have been immediately obvious that 2π and 6.28 were synonymous. And if you'd tried the calculation with both formulae you'd have seen where the difference in result was.

I'm guessing you're pretty young and inexperienced. Understood you're trying to get your head around this. It isn't easy but its going to get a lot harder if you're serious about getting into electronics.

 

OK, I don't normally reply to those that leap down my throat, but in my view of your question you seemed to be panicking, so I gave you the same advice I'd give any of my students. Maybe it wasn't obvious to you, but putting the two formulae side by side it should have been immediately obvious that 2π and 6.28 were synonymous. And if you'd tried the calculation with both formulae you'd have seen where the difference in result was.

I'm guessing you're pretty young and inexperienced. Understood you're trying to get your head around this. It isn't easy but its going to get a lot harder if you're serious about getting into electronics.

Where did you get the idea that I was panicking?

And it wasn’t obvious that’s why I was asking the questions…

Why don’t you just move on if you think I’m jumping down your throat. Seems like your the sort of guy that can dish it out but cant take it.[/QUOTE]

 

Where did you get the idea that I was panicking?

And it wasn’t obvious that’s why I was asking the questions…

Why don’t you just move on if you think I’m jumping down your throat. Seems like your the sort of guy that can dish it out but cant take it.

[/QUOTE]

Hello there,

Wow, that's some attitude you got there I can't help but mention that it won't help you learn more. Even if someone is overtly rude to you the best way to handle it is to reply in a sensible way not to fan the fire. I know it is not easy to do sometimes though.
Part of the learning process is to learn the best way to socially interact with other professionals, unless of course you want to become a politician
<insert really big chuckle here>

I think all he meant by 'take a breath' was to look the problem over again and see if there is anything logical that pops out at you.

What I have to do sometimes is take a break and come back to the problem later. I find this helps a lot. I can work on something for hours trying to figure it out not realizing that I am too tired at the moment. After even a short rest sometimes, I can come back and solve it within a few minutes.

Also, when your result comes out very close to the correct answer it usually means there is something just slightly off, so you start to look at differences and ratios. If you have a checking account and it does not balance, you can subtract the bank balance from your balance and almost immediately figure out that one item was left off the list accidentally, and everything works out. Thus, just looking a difference helps solve the problem easily.
Sometimes a ratio helps. looking at the ratio of the given answer and your answer, you can compare that to the ratio of 2*pi over 6.28 and see if that makes enough sense to solve the problem.

 

Time out to cool off.