Current flow across inductors in Series

In summary: There is no steady current in the circuit depicted. Were you hoping there'd be a steady current somewhere? If so, why?I was hoping there would be a steady current somewhere in the circuit because it would make it easier to calculate the time it takes for a steady current to flow through the inductor. But I understand that it's not always that simple.
  • #1
Samson4
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I can't articulately ask the question so I drew a diagram. In the diagram, both capacitors are equal in capacitance. The bottom inductors are both 10000 nh and the top are 100 nh.
A. Will the capacitors charge at the same time?
B If we switch the large inductors to the top and the small to the bottom of the diagram, will the capacitors charge at the same rate?
 

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  • #2
Can we assume that although it is not depicted, there exists some mechanism (a switch, possibly?) by which the circuit can be energized or de-energized at will?
 
  • #3
While ever there is a changing current in an inductor there will be a voltage loss across that inductor. So, after switch-on, the upper capacitor won't charge at a rate exactly identical with that of the lower one because of the additional impedance in the upper ones path (the pair of tiny 100nH inductors).
 
  • #4
brotherStefan said:
Can we assume that although it is not depicted, there exists some mechanism (a switch, possibly?) by which the circuit can be energized or de-energized at will?

Yes, I forgot to add it.
 
  • #5
NascentOxygen said:
While ever there is a changing current in an inductor there will be a voltage loss across that inductor. So, after switch-on, the upper capacitor won't charge at a rate exactly identical with that of the lower one because of the additional impedance in the upper ones path (the pair of tiny 100nH inductors).

Okay, now this is what I thought. But, will both inductors store energy in their magnetic fields before either capacitor begins to charge? Or will it be a first come first serve deal with the current flow?
 
  • #6
Samson4 said:
Okay, now this is what I thought. But, will both inductors store energy in their magnetic fields before either capacitor begins to charge?
The top capacitor charges as current flows to it via the top pair of inductors. Inductors store energy as current flows in them. The top pair of inductors are in series, so they share the same identical current, and their current is the current charging the top capacitor. So it all happens starting together.
 
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  • #7
Okay, now what determines the time it takes for a steady current to flow through an inductor? Is there a formula I can look up?
 
  • #8
Samson4 said:
Okay, now what determines the time it takes for a steady current to flow through an inductor? Is there a formula I can look up?
There is no steady current in the circuit depicted. Were you hoping there'd be a steady current somewhere? If so, why?
 
  • #9
Oh i know that. I meant in general, knowing the parameters of an inductor, how can we calculate the time it takes before a steady current will flow through it.
 
  • #10
Analysis is generally not a simple matter, even where the inductor is assumed ideal. The simplest case would be where you have an ideal inductor connected across an ideal voltage source---and here the current never reaches a steady value, it just goes on increasing at a fixed rate forever. If you now insert a resistor in series with the inductor, to create a 3 element circuit, then after switch-on the current increases but with a decaying exponential. You might consider that after 5 or more time-constants have elapsed the current is getting close to a steady value.

If you are unfamiliar with these terms, google for RL circuit time constant.
 
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FAQ: Current flow across inductors in Series

1. What is an inductor?

An inductor is an electrical component that can store energy in the form of a magnetic field. It is made up of a coil of wire, and when an electric current flows through it, a magnetic field is created.

2. What does it mean for inductors to be connected in series?

When inductors are connected in series, it means that they are connected one after the other, so that the same electric current flows through each of them in the same direction.

3. How does current flow across inductors in series?

Current flow across inductors in series is affected by the properties of inductance and capacitance. When an electric current is first applied, the inductors resist the change in current, causing a temporary increase in voltage. As the current stabilizes, the inductors allow the current to flow freely.

4. What happens when inductors in series have different inductances?

When inductors in series have different inductances, the total inductance of the series is equal to the sum of the individual inductances. This means that the total resistance to the change in current will be greater, resulting in a larger temporary increase in voltage.

5. How does current flow change across inductors in series at different frequencies?

At low frequencies, the inductors in series act as a single inductor with a combined inductance. However, at high frequencies, the inductors behave more like independent components with their own inductances. This can affect the amount of current that flows through each inductor and can lead to variations in voltage across the series.

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