Questions about how an inductor works

[jim hardy]

if the pot. difference across the resistor is zero how can current flow ?

okay since you insist on freeze-frame thinking
at the instant of startup
The current has , as i explained, two descriptors, magnitude zero and rate of change E/L
an instant later it has magnitude i and rate of change (E-iR)/L

What is difficult about that ?

 

[jim hardy]

at the instant of startup
The current has , as i explained, two descriptors, magnitude zero and rate of change E/L
an instant later it has magnitude i and rate of change (E-iR)/L

https://lh5.googleusercontent.com/gcL8fBozjbWPZ6G77g3f-fDKg9AWXa9DPUsOXgPFhUz9pRCFk2L1xdEVEt9x9v2ernjMA5bDKEfVMA=w1366-h658

try plotting a piecewise approximation.
Assign values of 1 volt 1 ohm and 1 henry
and discrete time steps of one millisecondAt t=0
current I = 0
voltage across resistor = 0
voltage across inductor = 1 volt
and rate of change of current (ΔI / ΔT) is (voltage across inductor)/L = 1volt/1henry = 1 amp per second.

At t = 1 millisecond (0.001)
current has increased from zero to zero + (rate of change X time elapsed)
new current I = 0 + 1 amp/sec X 0.001 sec = .001 amp
new voltage across resistor is I X R = 0,001 volts
new voltage across inductor is 1 - (volts across resistor) = 0.999 volts
and new rate of change of current is (voltage across inductor)/L = 0.999 amps /second

What are they at t= 2 mllliseconds ? 10 milliseconds ? One second ? (hint write a program to iterate a thousand times)

Do that exercise with pencil paper and calculator.
It's the only way you'll 'get it' .
That's how we mortals have to train our brain to think like Mother Nature.

And don't feel insulted - i had to do the same exact thing in my beginner days.
We non- genius types who question so hard become powerful thinkers if we don't give up.
But we do come to believe in calculus.

old jim

 

[jim hardy]

pls tell me all these in terms of electrons, force, electric-magnetic fields i.e., very basic

i want to understand it from the root
Please, please...

Then do the exercise in post 32.
We learn by doing not by reading about doing.

 

[AASHISH SRIVASTAVA]

thanks a lot sir you all helped me a lot in understanding it

 

[jim hardy]

thanks a lot sir you all helped me a lot in understanding it

I hope so.
I hope also you worked that stepwise approximation in post #32. It's the same thinking process we go through to learn basic calculus - keep making the steps smaller and smaller , approaching zero.
That helps us believe that calculus actually works.

 

[AASHISH SRIVASTAVA]

great thanks sir for your support but pls don't take me wrong till now we understood the inductor mathematically only. From start of this thread I wished to understand the inductor in terms of basic physics laws i.e., how magnetic field builds, how force on charge carriers comes to get into motion to make current.

My question was when a DC supply V (ideal) is suddenly connected to a series RL circuit then L has an electric field (Fe = -eE) how magnetic flux changed?, without current flow at start ---- then how induced emf = V comes(Fe = -eE) ? then further how the supply V overcomes this induced emf V (Fe = -eE)

I know mathematically ALL IS WELL but I want to know the PHYSICS of INDUCTOR

pls guide me

 

[jim hardy]

Hyperphysics does a pretty good job.

Laws of Ampere Faraday and Lenz are your starting point
they describe observed interactions of flux current and voltage.

You'll want to start at this site
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/indcon.html#c1
and follow these lessons.

That should get you started

it all goes back to force F on a charge Q moving relative to a magnetic field B equals QV cross* B
*cross being 'vector cross product'

 

[jim hardy]

how magnetic flux changed?, without current flow at start

Flux and current are in proportion. Both start from zero.

Just as when you apply force to an object at rest -
it immediately acquires acceleration (F=MA ),
its velocity starts from zero and increases
and its position changes at ever increasing rate.

You still refuse to believe in Mother Nature's derivative-integrals.

A charge in the wire experiences a force F along the wire due to the electric field E, F= qE.
So it accelerates down the wire.
As soon as the charge starts to move a magnetic field appears and begins to expand due to that charge's motion. That's Ampere's Law.
Relative motion between that expanding field and the moving charge produces a counter force on the charge F=qV_elocitycrossB that opposes its acceleration
and that's where counter-emf comes from.

An inductor is usually a solenoid of some sort.

 

[CWatters]

My question was when a DC supply V (ideal) is suddenly connected to a series RL circuit then L has an electric field (Fe = -eE) how magnetic flux changed, without current flow at start

Jim has given you some good reading material on the physics but I wanted to correct you on the above.

Consider a Voltage V applied directly to an inductor (no R in the circuit).

Take a look at the graph below. The top graph shows a voltage V applied "suddenly". The voltage increases from zero to V over time t₁ where t₁ is very short. Because it's short I have enlarged the horizontal scale so you can see what is happening.

The lower graph shows how the current changes over time t₁ and after. No matter how short t₁ the current will still increase as the voltage ramps up. So the current is small but not zero when voltage V has finished being applied. In addition it's already increasing as fast as it ever will.

After t₁ the current continues to increase, linearly now because V is a constant.

In a circuit with a series resistor R there is a corresponding voltage drop across the resistor due to the current flowing through it. At all times the inductor voltage is lower that the applied voltage.