beginner help

Dave

Joined Nov 17, 2003
6,970
If you're happy with the Branch Current Method, we could now move onto the Mesh Current Method - what is posing you the issue here?

(Incidently, if you still are having issues with the Branch Current Method let me know what they are first).

Dave
 

Thread Starter

chunkmartinez

Joined Jan 6, 2007
180
Actually solving the equations for both methods was my problem, but now that i can solve them, I can also inderstand the mesh method now. ..THANX..
 
Hi Dave, you've been very useful for me aswell. I was just wondering if you could help me with these questions.. I dont really understand the concept of complex numbers, i know its a representation of a number on the y axis but it dosn't really help me. Have also been having trouble with Node Voltages and Loop Current Analysis. I think the problem im having with loop currents is related to being unable to calculate the voltage drop accross each resistor (being that all the voltages around a closed circuit = 0 right?).

Joe :)
 

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Thread Starter

chunkmartinez

Joined Jan 6, 2007
180
Ok Ive moved my way on up to chapter 15, and now im having a little trouble with inductors. I Understood capacitors and how inductors are opposingly similar. But i don't understand why as current increases the voltage decreases.
 

Distort10n

Joined Dec 25, 2006
429
Ok Ive moved my way on up to chapter 15, and now im having a little trouble with inductors. I Understood capacitors and how inductors are opposingly similar. But i don't understand why as current increases the voltage decreases.
V(L) = L di/dt :)

The larger rate of change of current through an inductor, then the larger the voltage. When you reach a constant current, your voltage would be zero. That is why an inductor is an ideal short at DC steady state.
 

Dave

Joined Nov 17, 2003
6,970
Hi Dave, you've been very useful for me aswell. I was just wondering if you could help me with these questions.. I dont really understand the concept of complex numbers, i know its a representation of a number on the y axis but it dosn't really help me. Have also been having trouble with Node Voltages and Loop Current Analysis. I think the problem im having with loop currents is related to being unable to calculate the voltage drop accross each resistor (being that all the voltages around a closed circuit = 0 right?).

Joe :)
Hi Joe,

I have seen your question in this thread about complex numbers and analysing circuits. Ask your questions on this subject in that thread. As for not understanding Node Voltage and Loop Current Analysis, I recommend you start a new thread with your query, that way we don't end up getting our wires crossed between your questions and chunkmartinez's questions.

Ok Ive moved my way on up to chapter 15, and now im having a little trouble with inductors. I Understood capacitors and how inductors are opposingly similar. But i don't understand why as current increases the voltage decreases.
knightofsolamnus has provided the answer to this question. The reasons as to why are in the realms on EM theory, which is possibly beyond the scope of what you are trying to understand.

Glad to here you have understood the Branch Current and Mesh Current methods.

Dave
 

Distort10n

Joined Dec 25, 2006
429
how do inductors self-induce voltage? & why does the voltage flow in the opposing direction as the current?
They 'self' induce voltage because of the flow of current which produces a magnetic field. The potential difference across the inductor, the electric field, is the voltage.
If you write the differential equation, you can easily see why the polarity flips. This is why you often see a diode across and inductor or a relay because of inductive 'kick.'
 

Thread Starter

chunkmartinez

Joined Jan 6, 2007
180
They 'self' induce voltage because of the flow of current which produces a magnetic field. The potential difference across the inductor, the electric field, is the voltage.
I still dont exactly understand how the polarity flips. And also, does this polarity flip cause resistance? and would this resistance be the cause of the current staying constant?
 

Dave

Joined Nov 17, 2003
6,970
Hi chunkmartinez,

This principle is referred to as Lenz's Law which states that direction of current flow in the inductor is such that it opposes the change to which it is due - sounds like a load of cobblers, but it essentially means inductors are designed to oppose changes in current flowing through the inductor, by dropping a voltage that is directly proportional to the current, hence:

v = L(di/dt)

By definition that is what an inductor does. You should look at Volume 2 - Chapter 2 for further reading, (particular this section).

As for resistance in an inductor, you are correct to state that a "real" inductor would have resistance by the very nature of the fact that it is a wire, which we know will have some form of resistance associated. If you are looking at a "real" inductor then you would model it as an inductor and resistor in series, hence:

v = L(di/dt) + iR

Where R is the associated resistance of the inductor wire.

You won't be the first to fine it difficult to understand how inductors work. The big problem is that you have to really think about the electromagnetics of inductors to truely understand what is happening, and sometimes this makes the situation considerably more complicated than needs be. You may just need to take a leap of faith on this one.

Dave
 

italo

Joined Nov 20, 2005
205
a voltage source can be defined as an infinite inpedance source as opposed to a current source which can be defined as a zero inpedance source. A coil is a storage component it stores current as opposed to cap. Also once the current is released the polarity will change rule of thumb therefore a negative spike minus losses. And again and again until it dissipates its energy
 

Thread Starter

chunkmartinez

Joined Jan 6, 2007
180
a voltage source can be defined as an infinite inpedance source as opposed to a current source which can be defined as a zero inpedance source. A coil is a storage component it stores current as opposed to cap. Also once the current is released the polarity will change rule of thumb therefore a negative spike minus losses. And again and again until it dissipates its energy
Really? voltage can be defined as resistance?
 

Dave

Joined Nov 17, 2003
6,970
You know a conductor carrying a current produces a magnetic field (and hence flux) that is related to the amount of current flowing the conductor (ref. Ampere's Law). Now consider that conductor in an inductor-type arrangement. Any changes in the current flowing through the conductor will lead to a change the flux that will generate a time-varying EMF or voltage (ref. Faraday's Law) that will act such to oppose the change in current (ref. Lenz's Law). So for an increase in the time variation of the current (di/dt) the change in flux generated will cause an increase in the opposing EMF to counteract the increase in (di/dt), and vice versa. If the current is not changing (di/dt = 0) then the opposing EMF will be zero, hence the relationship:

v(t) = L(di/dt)

As stated previously, the conducting wire will have some finite resistance, so for real inductors the relationship is:

v(t) = L(di/dt) + iR

And hence for di/dt = 0, the inductor behaves like a resistor.

Dave
 

Murod

Joined Dec 24, 2005
30
When you apply an ideal voltage source to an ideal inductor (zero resistance), it's analog to applying a force to a mass in ideal environment (no friction).

At the begining of a time line
Current is zero, and mass's velocity is not exist

Then the current start to increase
And the velocity begin to grow

In the name of universe's balance
Every changing power should be fight
Changed current in an inductor must generate opposite voltage
Changed velocity of a mass must produce opposite force
Those opposition make your voltmeter swing
And make you feel your own force when you throw a ball

Keep the voltage to increase the current bigger and bigger
Keep the force to move the mass faster and faster
The current and the velocity will go to the infinity
Keep going without ending

Actually there are no ideal condition in real life. Why inductor can store an electric energy, it's similar to mass can store kinetic energy. Imagine you can apply a force to a mass in a no-friction environment, like in an outer space with no air friction, no gravity, the mass will accelerate and when you stop applying the force then the mass will keep moving in a constant velocity, the mass will store the energy that we apply. Imagine that we have an inductor with zero resistance. Apply a voltage to accelerate the electron inside, in other words to increase the current, and at certain point stop applying the voltage and connect (short) the inductor itself to bypass the electron from one end to the other end of the inductor, the current will flow forever. With super conductor (not ideal conductor), the electron will gradually slowing down, the current gradually decrease and turn into heat before completely stop flowing in few days.

Hasan Murod.
 

sparkfishes

Joined Oct 19, 2009
16
I find it easier to explain ( or think) of electricity as I would water
The wire are hoses, resistors valves,Volts is = pressure
Amps is volume of the flow ( buckets per second)

High pressure + big valve opening = High flow ( 10 Buckets)
is the same as
High Volts + LOW resitance=high amps ( say 10 amps)

High pressure + small valve opening = less flow ( 3 buckets)
is the same as
High Volts + High Resistance = less amps ( say 3A)




Medium Pressure + big valve open= larger flow(2 full buckets)
Medium Volt + LOW resistance = 2amps


Low Pressure + small valve opening = low flow ( 1/10 of a bucket)
Low volts+ high Resistance = low amps ( 0.1amp)

I hope that hep visualise the problem - and not make it worse
 
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