Hi guys. Im in australia and completing my first yr of study toward my electricians licence. When I was younger I received a rock to the head which left me with damage to parts of my learning receptors in my brain. I now learn better from my own techiques which is a little frustrating as most dont learn in these same techniques meaning the edcation programs set and teaching plans cant really be catered for the minority such as myself. I was exempt for the first half of the yr due to some recognised prior learning as I am a refrigeration mechanic but now find myself in a situation where I am a bit behind with the rest of the students. We have some exams coming up next week and I am having troubles with the working out of some of the basic circuit equations regarding electro magnetic fields. I am gathering that this site is more for the engineers to discuss far more advanced problems or situations but I was hoping for some showing of the working out of problems. We have been fortunant to be given the equations but when your in the dark its a bit like reading a differant language! I was wondering if I posted a few of these problems would there be someone on this site that could help show the breakdown of calculations? If that is not really what this site is for I really don't want to waste anyones time and would then ask if anyone knew of any other sites that I could go to for help? For all the engineers out there WELL DONE! I dont think my mind could take to many more levels of this! Thanks for your time.

 

Hey jasmc,

Welcome to All About Circuits (AAC)!

We're very glad you became a member and we promise to help you with anything you would like to know (If we have the answer, and there are many here who do)! Just type in a question and we'll all do our best to help you. Do you have a specific question you'd like answered?

 

A rock to the head. Wow. What horrible person did that to you?

And this site is for people of different levels. There are people here who are just learning what electricity is, as well as more advanced people. We can help you with anything, so go ahead and ask.

 

Ok guys you wont blieve this but I have just writen a post back which was not that long but took me just over 3 hrs and when I went to submit it it wiped the whole thing.......... AAAAAAAAAAAAAAAAAAHHHHHHHHHHHHH

Really quick version

My test is tommorow and we have been on holidays for the past 2 weeks so I havnt been able to talk to anyone about these. I tried one person who was a teaching this last year in another stae and he couldnt get the same answers that were given in our booklets!

Its regarding a symple magnetic circuit
Number of turns = 400
Current I = 4A
csa a = 900mm2
Length of iron path li 1250mm
Length of air gap lg = 1.5mm
Relative permeability of iron core uir = 1200
Permability of air = 12.57 x 10-7
Permeability of air ura = 1.0


Calculate the m.m.f of the coil
My answer
FM = IN FM = 4A x 400t = 1600At

2. The reluctance of the magnetic path

Rm = L / μo x μr x a

Rm = 1250 x 10-3 / 1257 x 10-7 x 1200 x 900 x 10-6
Rm = 1.25 / 135756
Rm = 920769.6161 (the answer in the book was 921000At/Wb, did they just round it out or did i Calculate incorect?)

3.The reluctance of the air gap.
My answer
Rm = L / μo x μr x a

Rm = 1.5 x 10-3 / 12.57 x 10-7 x 1 x 900x 10-6
Rm = .0015 / 1.1313-9
Rm = 1325908.247 (the answer in the book was 1330000At/Wb, did they just round it out or did i Calculate incorect?)

4.The total flux
My answer
Fx = Fm/S (I could not find the symbol for flux so just using Fx)
Fx = 1600 At / H.E.L.P !!
The answer given in the book is 711μWb meaning the reluctance was 2.25031617 but I can not figure out where that number has come from)

5. The flux density
B = Fx/a
B = 711μWb / 900
B = .79T

Just need to know if my working are correct or if I should be showing anything differantly.

Thanks so much for helping me out

 

Meant to say thanks to count volta for the concern about the injury but much as it was serious neuro injury it was actually in harmelss fun from school accident (rock thrown as a joke and I got in its way)back when I was 10. After that time I had to learn to read, write count and talk again but it turned out that one of the parts of the brain that was mainly used for filtration and passage for thought process took over and grew into a learning receptor ( got me in a couple of medical mags for it!) I cant explain how I learn things now but I have figured it out. Since that time been successful in my business and lived a great full life without anyone knowing about any past injury. That usually drove the teachers mad though seeing as though the harder they worked the less it sunk in yet come exam times marks were pretty good! If I dont make it through the exams this season Ill start again next year and get it right.

 

Add the two reluctance values

Rtot= Rmcore+Rgap=920769.6161+1325908.247=2.2467e^6

Hence Fx=1600/2.2467e^6=712.16uWb

That's it.

 

Re losing all that work - hard luck! I know how you feel on that score. May I suggest you don't write too much in any one post. Keep it short and you have the advantage of your readers not having to wade through a long dissertation.

Also it's a good idea to start a new thread once the topic changes - as it appears to have done here.

Happy to be of help anytime. Cheers. t_n_k

 

Thankyou !!!!