newbie needs help!!!!

Discussion in 'General Electronics Chat' started by Ridgy, Oct 14, 2009.

  1. Ridgy

    Thread Starter New Member

    Oct 14, 2009
    3
    0
    I have looked thru the forum & haven't really found anything relavant to my question. I am learning component level electronics (just started few months), I know what an inductor does but can someone put in really, really simple terms what inductance is( like reactance is similar resistance, inductance is similar to ?), I am having trouble as the course is very intensive and the lecturer isn't very good as he is new & finds it hard to explain things. thnx in advance for any help, oh knowledgable ones:D
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    This post should have been in the chat forum, but here goes.

    A coil is the opposite of a capacitor. A capacitor goes to the voltage of the source, and stores energy as an electric field. A coil goes to the current of the source, and stores energy as a magnetic field. It is probably no coincidence that to make or sense an electromagnetic wave it takes a coil and capacitor together.
     
  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    I'll put in really simple.
    As resistance is to DC ( although it is also to AC ), Inductance is mainly a resistive force to AC only.
    Inductors have two types of resistance effect.
    One is the Inductive reactance that opposes AC in AC circuits.
    Two is that the Inductor also has a DC resistance ( which is the DC resistance of the coil ) which is always negligible to AC ( in most cases ), instead the Inductance always effects AC.

    for eg: If a DC voltage has an AC super imposed in it like a ripple in a DC voltage, an Inductor can be used to Block the AC and let a low resistive path to the DC, thus eleminating the AC component in the DC Voltage.

    Rifaa
     
  4. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    How about this?

    Electricity is subject to three effects when it interacts with matter.

    Capacitance

    Inductance

    Resistance

    I have put them in this order because electricity can be static or in motion.

    Capacitance is the only interaction of the three in play when we consider static electricity.
    All three cause effects when we consider electricity in motion.

    We have names for these interactions, the two main ones of interest here are:-

    Electrostatic and Magnetic.

    These interactions can both produce real forces on matter. Forces that can move mass and do work.
    If you know any mechanics you will understand the statement that these interactions are at right angles to each other and therefore do not directly affect each other ie the are independent.

    Although a simpler concept to present the third interaction, resistive, is much harder to explain theoretically as it is an energy effect and requires some more advanced physics. So I won't go into it further.

    Broadly speaking the electrostatic interaction is responsible for capacitance

    and the (electro) magnetic interaction is responsible for inductance.

    So capacitance applies to both static and moving electricity.

    However inductance only applies to moving electricity.

    You will note I haven't used the terms AC or DC electricty as it is not true to say that capacitance and inductance only apply to AC circuits.

    Both represent a form of electricity in motion, and both display capacitive, resistive and inductive effects.
     
    Last edited: Oct 14, 2009
  5. Ratch

    New Member

    Mar 20, 2007
    1,068
    3
    R!f@@,

    No, inductance is not a resistance and resistance is not a "force". Inductance and resistance impede (impedance) current by two entirely different mechanisms. A resistor impedes current by dissipating the energy of the moving charges into heat, thereby lowering the voltage (energy density) of the charge. An inductance uses the energy of the moving charges to build a magnetic field where the energy is stored. While the field is increasing, it induces a back voltage that lowers the current through the coil. When the current stops changing, the magnetic field collapses and assists the voltage that was used to first build up the magnetic field. In summary, energy dissipated by a resistor is lost from the circuit as heat, but the energy "borrowed" from the circuit to build the magnetic field is eventually given back for a zero sum gain/loss.

    Wrong. Inductance affects (not effects) any circuit when current change is present, whether AC or not.

    Ratch
     
  6. Ratch

    New Member

    Mar 20, 2007
    1,068
    3
    Ridgy,

    Inductance is the constant of proportionality that relates the change of current to voltage. Any change in current through a component with inductance, such as a coil, will induce a voltage across that component. A component with a higher constant of proportionality (inductance) will induce a higher voltage. The formula is -V = L*dI/dt, where is L is the constant of of proportionality (inductance) and dI/dt the the current change with respect to time.

    Ratch
     
  7. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
    1,758
    98
    Did the OP delete some messages?
     
  8. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Naw, people overexplaining a simple question. :D
     
  9. wr8y

    Active Member

    Sep 16, 2008
    232
    1
    I sure like this! :cool:

    BUT:

    But could we not just explain to the OPer that inductance is the opposition to current flow resulting from the electromagnetic effects in a coil or piece of wire?

    Could we then go on to explain that the current thru the conductor sets up lines of force, and these very lines of force cut thru the conductor and oppose the current in the conductor?

    That is, the opposition to current flow that IS inductance is caused by the very current that created the lines of force in the first place.

    Now, how did I do? Bill - what ya think of that?
     
    Last edited: Oct 14, 2009
  10. hobbyist

    Distinguished Member

    Aug 10, 2008
    764
    56

    Inductance in a AC circuit ,
    is
    Similar to resistance in a DC circuit.

    They both restrict the flow of current.
     
  11. Ratch

    New Member

    Mar 20, 2007
    1,068
    3
    hobbyist,

    The flow of charge you mean. And for half the AC cycle, it aids the flow of charge when the magnetic field collapses.

    Ratch
     
  12. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    We could not because we may not be interested in current.
    We may only be interested in the magnetic field generated, which depends upon the inductance, (and the current I know but we may simply say we will supply whatever current is needed).

    An example of this is also a good example of inductance in a DC circuit. That is the humble battery operated electric door bell.
    Here the current in the inductor coil produces the magnetic field which drives the bell hammer. We don't care what that is so long as it is enough to operate the hammer.
     
  13. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    This discussion was not what the OP (original thread - http://forum.allaboutcircuits.com/showthread.php?t=28764) was looking for.

    I realize the continuity is a bit broken, but this deserves its own thread.

    By the way, nit-picking like -
    - does not contribute meaningfully.
     
    Last edited: Oct 14, 2009
  14. ELECTRONERD

    Senior Member

    May 26, 2009
    1,146
    16
    Starting a new thread like that, Ratch, is confusing for others. The only reason I didn't find it confusing is because I read the previous posts posted in the other forum. You can well imagine the difficulty a new person might have all of the sudden coming to this forum. "When did they say this?" "What thread did this originally come from?"
     
  15. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Not at all - the switcheroo was a moderator action, as the topic was going away from the OP's question. Notice the link.
     
  16. ELECTRONERD

    Senior Member

    May 26, 2009
    1,146
    16
    Ah...I see. Well in that case, it's perfectly fine! :D
     
  17. Ratch

    New Member

    Mar 20, 2007
    1,068
    3
    beenthere,

    What I don't understand is why post #2 of this thread was moved. It answered the OPs question directly and concisely. Perhaps you should consider moving it back to where it was.

    Ratch
     
  18. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    I nearly wrote in the other thread that this is a time when I find myself in full agreement with Ratch.

    You have moved two posts counteracting the wrong assertion by several members, who should know better, that inductance (and capacitance) is only associated with AC circuitry.

    Further there is the unrefuted paradoxical statement that inductance provide 'impedance in AC circuits like resistance provides it' in DC.

    This coupled with (valid) assertions that resistance also acts in AC circuits must be very confusing for a beginner.

    In my initial explanation post I also avoided 'voltage', 'current', AC and DC as I didn't know the state of the OP's knowledge, an I thought my screed was already long enough.

    I would be happy to expand upon my homespun explanations in another thread as at least one viewer liked them, but things are rather disjoint as they stand at the moment.
     
  19. bundick

    Active Member

    Dec 19, 2007
    97
    1
    Thanks to Ratch for a great explanation of the difference between Induction and resistance. After some time in School, I felt some instructors could never explain how to tie shoes, let alone something the students were ignorant of.
    Where was Ratch when I needed him?
     
  20. ELECTRONERD

    Senior Member

    May 26, 2009
    1,146
    16
    Ha, ha, ha...;) Yep, we're definitely glad to have Ratch around here, to set us all straight! I've probably learned most of my electronic theory from him!
     
Loading...