# Question on Inductance/inductor

Discussion in 'General Electronics Chat' started by tony8404, Feb 23, 2009.

1. ### tony8404 Thread Starter Active Member

Jun 11, 2008
98
0
Hello everyone hope all is well with you... I did not read over this weekend like i wanted to, a result of this now is that i feel i have forgotten or did not understand everything i read on Inductance/inductors. My book has a pretty good section on the subject but i am confused. Can anyone explain to me Inductance/Inductors in simple terms??? I try to look for something on the internet along the lines of easy explenation ect.. ect.. but no luck.

I understand that Inductance happens due to the magnetic field in an inductor or conductor.
I understand that the magnetic fields cross into each other and create one field in an inductor.
I understand that it expands up to the maxium ohms law value, and once the value is met inductance holds or stops until a change in current...
I understand that it also collapses.
I understand what it takes out of the source it puts back into the source.
I understand that Inductance tries to keep current up and tries to keep if from going down.

is this really all there is to inductance besides the formulas? I feel i am missing something... to me it seems like i really need to know this part before i can go on. If anyone has some patience or knows how to explain the whole thing please, please help me... thank you sooo much.

P.S i have watched the videos in the video section on inductance and to me it just seems like that cannot be all there is to it. maybe i am wrong

2. ### wilson479 New Member

Feb 23, 2009
5
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When you pass a current through a conductor, such as a wire, a magnetic field is set up around the wire.

The size and strength of the field is dependant on the conductor material and cross sectional area, as well as current applied. You can make coils out of the wire and introduce magnets to generate an even more powerful field.

When the supply voltage is removed, the magnetic field collapses back into the conductor (wire), causing a voltage of equal and opposite polarity to the original supply to be generated. This voltage is known as back emf.

Basically a capacitor stores charge and an inductor stores voltage.

Hope this makes sense?

Apr 5, 2008
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4. ### tony8404 Thread Starter Active Member

Jun 11, 2008
98
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Wilson, i understand everything you typed in your post, pretty much what i learned or read in my book... Question though, is that all that is needed to know about inductance besides the formulas? I do not know why but for some reason i feel that cannot be it but i hope so lol..

Bertus, thank you for the links, i am going to check them out, give me a little bit to check em out and i will reply with any questions.... Thanks again bertus..

5. ### wilson479 New Member

Feb 23, 2009
5
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Hi Tony,

When I was first learning electronics, we where force fed purely DC theory for a long time. Therefore capacitors seemed a mystery to me, and inductors where an even bigger mystery for years after!

If you begin reading the Volume II chapter - "AC" on this site, you will hopefully get a much better understanding of these two components and the ways they are used.

Basically, capacitors and inductors create some "resistance" to the AC currrent flow in a circuit. This "resistance" varies depending on the frequency of the applied current.

If you apply a high frequency signal; a capacitor will act as a small resistance. At a low frequency, the capacitor will be high resistance.

An inductor is the opposite; high frequency is high resistance, low frequency is low resistance.

So these inductors and capacitors can be used together or with normal resistors to create AC voltage dividers and other types of "filter" which can direct certain frequencies where we want them to go.

You can do cool things like filters, resonant circuits, oscilators.

The only formula you really need to know at the moment is for calculating the AC "resistance" (really called reactance) of an inductor. This is:

Code ( (Unknown Language)):
1.
2. Xc = 2∏fL
3.
4. Where Xc = Equivalent AC resistance
5. ∏ = Pi (3.14159)
6. f = input frequency
7. L = Inductor value in Henrys
8.
To give you an example,

If you have a 10kΩ resistor connected in series to a 16H inductor, and we apply a voltage of say 10V @ 100Hz (sine wave); The eqivalent AC resistance of the inductor will be 2∏100*16 = 10kΩ.

As the two "resistances" are equal, they will both drop an equal amount of the supply voltage and the point between them will be half of the supply.

You can plug higher and lower value input frequencies into the formula to see how the output will be affected.

*I should say that Resistance is a DC term. The "resistance" of a capacitor or inductor is called its "reactance".

When diffrent types of resistance and reactance are mixed in a circuit, it is known as impedance.

Hope this helps?

6. ### tony8404 Thread Starter Active Member

Jun 11, 2008
98
0
Wilson479, I have been using this site as if i paid for a membership getting every half penny of info i can get.. Not only am i reading a basic electricity book, i am also reading off of this site going along with my book and i will tell you another thing. I read in my book, if i question something or do not understand it fully I do not go on. I then go here and read that section, then i go to the video section and that really helps. Usually by then I have it down.

Since you described how you first learned electronics, made me think of me. I also, had dc spoon fed at my school and when ac came along not so much so i did not understand and got confused. Well, now i am gonna take a break from the school for another month or two and learn on my own. I do know a bit about the basics of ac but when inductance and capacitance came about i did not understand and the class went to fast. but now that i read my butt off last night i know understand capacitor/capcitance and am re-reading inductance and i am now grasping it.

Question on formulas since you mentioned them... you say i only need the formula right now that you showed me and i have been trying to put that into my head when i found it in my reading. I am wondering what other formulas do i really need to know and which ones i do not.. here are some in my book and i feel some i do not need to know but want to make sure. Here are 4 formulas that were in the inductance part of my book that i question

- Counter EMF= -L*I/T
- L(henry's)= .4 *TT(pie)*N2*A*U

TIME CONSTANT -- L/R

- XL = 2*TT*F*L

Not to mention when you said this "
*I should say that Resistance is a DC term. The "resistance" of a capacitor or inductor is called its "reactance".

When diffrent types of resistance and reactance are mixed in a circuit, it is known as impedance.

Hope this helps? My freind you have no clue how much that helped LOL thankyou

7. ### wilson479 New Member

Feb 23, 2009
5
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Hi Tony,

I am glad to help, as I am still a student myself it prooves at least some of the hours I have been putting into the subject!

As for formulas, well its best to not try and learn them from memory. When you need to solve some problem, turn back to your book and read the chapter again.

This repetition of looking up the formula when needed really is the best way forward, unless you have a photographic memory of course!

Why not think about enrolling on a part time or evening class at your local college?

I have been studying two evenings per week for the last two years and have now nearly completed my foundation degree.

Its much easier to learn with support, and good fun at the same time.

Good luck what ever you choose!

8. ### tony8404 Thread Starter Active Member

Jun 11, 2008
98
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Well, the tradeschool i am attending is 3 nights a week from 6-10:30 p.m. I am currently out of the school right now due to switching programs. The program i was in was just like working for dishnetwork which you can due right out of highschool, not to mention that program has more classes to take and cost almost 4,000 then the electrical construction maintenance program. There is a total of ten classes and i am already done with 5 of them so i have about half year left. but i do not want to go back yet until i have the foundation like you have. I just do not want to struggle and be lost. especially with full time job and family i dont have the study time like i would like to have. Really cannot afford to be lost in this subject especially since i pay for it lol....

What i am going to do is start writing down the formulas with descriptions and every day i am going to start to look it over and sooner or later i will be able to sit down and write it out. but i like your approach as well due to the re-reading which i like because sometimes i read it again it makes better sense. i probably wont go back to school for another two months. I am gonna start to use multism 9 along with my studies.