# Why Does Adding a Coil Decrease Current in a Circuit?

• GoodEngineering
In summary: Also, the confusion starts with the terminology used. A coil in an AC circuit has inductive reactance, which is the opposition to the flow of current. This means that as the current increases, the voltage across the coil decreases. In DC, the coil has resistance rather than inductive reactance, which means it will oppose the current more.
GoodEngineering
TL;DR Summary
Why does the current decrease if added a coil?
Hello, so today I in my electrical machines class the teacher said that if we add a coil on a cicuit the total current will be less compared with a circuit with no coil included. Also if we replace a coil with (for example) 100 spirals with another with 300 spirals, the total current going through the circuit will be less. Example:

The teacher hasnt explained to us the math behind this, so right now I'm unable to solve this, Nevertherless, that's not what I'm looking for. He told us while we were in the class that this occurs because the magnetic field slows the current down, later on when the class was over I asked him for more information about this phenomenon, & told me that the current actually converts into a magnetic field.

Of course this second declaration left me confused & this is why I post this.

So can anyone tell me clearly why & how the current decrease when we add a coil in the circuit?

Nowhere do I see the magic acronym "A. C." or mention of frequency. You do understand that these effects all require dynamics, yes?
Also a "magnetic circuit" describes a pathway for magnetism, so the nomenclature is usually a circuit with inductors.

Those examples are terrible and wrong because the don't mention time.

The voltage across an inductor (coil) is proportional to the time rate of change of current. So it slows down the rate of increase of current. If the current is steady, the coil does nothing.

GoodEngineering said:
Hello, so today I in my electrical machines class the teacher said that if we add a coil on a cicuit the total current will be less compared with a circuit with no coil included. Also if we replace a coil with (for example) 100 spirals with another with 300 spirals, the total current going through the circuit will be less.
Have you had differential equations in your studies so far? The relationship between the voltage across an inductor and the current through it are related by the well-known differential equation:

$$v(t) = L [\frac{di(t)}{dt}]$$

That explains why more turns (higher inductance) lowers the AC current through a coil...

Well I think I forgot to say that it is DC, not AC.
This is why I was curious. Of course I know that coils in AC have a resistance, rather inductive reactance.

davenn
Oh my!

An instructor that needs instructing?

Who would have thought!

berkeman
I think you may have misunderstood something, or perhaps your instructor didn't explain what he really meant. As others have said, this doesn't really make sense for a DC circuit.
It's hard for us to explain what an inductor is and how it works if you aren't at that point in your studies. Unfortunately, there are a lot of "practical" or "vocational" electronics classes that do a really poor job of teaching what inductors and capacitors really are. These components respond to the rate of change of the voltage and/or current in the circuit. This means that the best understanding of them comes after you have studied a little bit of calculus.

GoodEngineering said:
Well I think I forgot to say that it is DC, not AC.

OK

GoodEngineering said:
Of course I know that coils in AC have a resistance, rather inductive reactance.

no, not correct, the other way around

Coils in DC have resistance rather than inductive reactance that they do with AC
DaveE said:
As others have said, this doesn't really make sense for a DC circuit.

of course it makes sense with DC
Adding a coil, is just adding extra resistance, and therefore the current through the circuit drops
as stated in post #1. There will be other effects as the magnetic field is generated

It seems everyone that responded has wrongly assumed AC

GoodEngineering

## 1. Why does adding a coil decrease current in a circuit?

Adding a coil to a circuit increases the overall resistance, which in turn decreases the current flow. This is due to the fact that the coil has its own resistance that must be overcome by the current, leading to a decrease in the overall current in the circuit.

## 2. How does a coil affect the flow of current in a circuit?

A coil, also known as an inductor, resists changes in the current flow through it. This means that when current flows through the coil, it creates a magnetic field which opposes the current flow, ultimately decreasing the overall current in the circuit.

## 3. Can a coil increase current in a circuit?

No, a coil cannot increase current in a circuit. As mentioned before, the coil has its own resistance that must be overcome by the current, leading to a decrease in the overall current in the circuit.

## 4. How does the number of coils in a circuit affect the current?

The number of coils in a circuit can affect the current by increasing the overall resistance in the circuit. This is because each coil adds its own resistance, and the more coils there are, the higher the resistance will be, resulting in a decrease in current flow.

## 5. Is there a way to counteract the decrease in current caused by a coil?

Yes, there are ways to counteract the decrease in current caused by a coil. One way is to add a capacitor in parallel with the coil, which can help to reduce the overall resistance in the circuit. Additionally, using a higher voltage source can also help to maintain a higher current flow in the circuit.

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