# basic defnitions

On Aug 27, 1:05 am, snipped-for-privacy@cs.ubc.ca (Dave Martindale) wrote:

yes sir..i understand it well but i am not yet convinced with what i have learned.Can you help me?
Ram
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sir i don't know how far you have understood my problem.Whether i haven't conveyed the meaning properly i am trying to say or my english usage...
Inductance may be defined as,the ratio of the magnetic flux to the current...which everyone knew that..what i need is that why the inductance should develop a magnetic energy around it..the energy may be in some other form..Similarly the capacitor it develops potential and now storing this potential will be of great use ...These have gained a lot of importance these days(and will continue in future also)..because of its power absorbing and delivering capacity...hope still researches are going on to reduce the power consumed by it! so i thought of gaining a still deeper knowledge of that..so only i posted this question..sorry if i had hurt you in anyway.....
Ram
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You haven't hurt me in any way. Now you have stated your problem more clearly, it appears that you are having a problem with the relationship between an electric current in a wire and the magnetic flux produced (Ampere's Law) (it is not the inductance that develops a magnetic field but the current and inductance is simply a measure of this. Observations were made, many years ago, and after various refinements and considerations, Ampere's Law and then Maxwell's equations were developed and do a good job of quantifying and expressing these relationships mathematically. Other relationships (Faraday) deal with voltage produced by a time rate of change of flux. We can put these relationships into a mathematical form and test the calculated behaviour for a variety of cases against the measured data. If it fails- then back to re-evaluate the mathematical model. ( For example circuit analysis using lumped parameters such as L,C are useful where physical distances are small compared to a wavelength. For high frequencies they may not be useful and Maxwell's equations have to be used. ) These do not go into <why> a current produces a magnetic field (and are based on the fact that it does) but there are theories that deal with this but these go beyond anything that I wish to deal with here. Similarly the relationships between charge and voltage led to a mathematical model which we use. Using these models leads to expressions for energy stored. These expressions are analogous to the expressions for energy stored in a spring or mass.
What is your knowledge of calculus? A basic knowledge of this would help considerably. There are also many circuits texts that go into this. I have, however, a feeling that you have this knowledge in rinciple and are trying to dig deeper- such as why a current produces a magnetic field (which I deliberately have not answered as it does require deeper concepts which haven't been proven.
--

Don Kelly snipped-for-privacy@shawcross.ca
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i'm bit strong in calculus...fine..the explanations were something different to that i heard of....everyone knows that current in an inductor lag the applied voltage by 90(degrees).....the books i referred so far give only the statements while others just prove it by mathematical model as you say...What i expect is that can all these basics could be proved without using mathematical models...
For the above question,i think this might be appreciable one..."the reason is based upon the law of inertia"..slightly modifying it...an object does not exhibit its property unless otherwise acted by an external force and it continues to remain as long as the drive exists......
When the voltage is applied across the inductor(from here it is dealt as coil),the coil will not allow the current at the instant of switching(i.e t = 0)..(coil though a conductor will not allow the current at t = 0 as the time is too short for the coil to exhibit its property)so no current flows..this is merely an open circuit..so the total voltage impressed is obtained....voltage is maximum and the current zero...then at the next moment the coil starts to allow the flow as it was unable to resist the change(or flow of current)....hence the current increases and the voltage impressed decreases.....hence current in an inductor lags the applied voltage by 90.....Is the above reason seem to validate it?
Yours sincerely Ram
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Elec Eng 101 starts at a College near you soon. But then first you need to fullfill the entry level requirements. (? Requirements ? Big word?)
John G.
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ram27 wrote:

The 'definitions' are exactly what you read in the text book. To ask for a different 'definition' is like asking to change the Oxford dictionary.
If what you meant is you don't understand the definitions given in the text books and would like some help understanding them, that's a slightly different question.
To understand these terms you need to start with 'inductance' and 'capacitance'. And to understand those, you should start with basic electrostatics and electro-magnetics. The other terms are off-shoots from these two basic physical phenomena.
daestrom
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================================================Hello Ram. We all remember the instant that the 'light bulb' turns on and we understand how something works. You can reach that point perhaps by collecting a signal generator, a scope, and an assortment of Ls, Cs and Rs, and tinkering with them. I used the concept that they are all resistors, its just the the Ls and Cs had resistance that varies with frequency. In EE school they told us the story of ELI the ICE man.
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BobG wrote:

I still use that when I teach PE exam review classes. Some things just can't be improved!
--
Benjamin D Miller, PE
www.bmillerengineering.com
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and what's wrong with the word 'CIVIL'?