Why doesn't an inductor act as a closed circuit to AC?

In summary: So if you have a large inductor and a small AC voltage (or vice versa), it will have a smaller effect on the current flowing through it then if you had a small inductor and a large AC voltage.In summary, an inductor resists a change in current by creating a voltage difference proportional to the rate of change. This is true for DC as well as AC.
  • #1
Vishera
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1
I understand that an inductor acts as a closed circuit to DC because it's just a coiled wire but why doesn't it act the same way for AC? What does it act as in AC?
 
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  • #2
You can think of the inductor as working a bit like inertia in stream of fluid: when the rate of flow changes, it 'resists' the change. It creates a voltage difference proportional to the rate of change in current - so when the current is constant then there is no voltage.
 
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  • #3
NateTG said:
You can think of the inductor as working a bit like inertia in stream of fluid: when the rate of flow changes, it 'resists' the change. It creates a voltage difference proportional to the rate of change in current - so when the current is constant then there is no voltage.

Wow. That was elegantly explained.
 
  • #4
Couple different ways to look at this.
The impedance of a INDUCTOR is JWL

w=omega...or radians per second of your input signal...such as the 377 in a wall outlet: 170sin377t volts
So clearly, as the frequency changes, so does the impedance.

What's the frequency of DC? Zero right? When you plug zero into JWL, you get zero resistance, or a "closed" circuit as you say above.

Then there is this formula:
L*di/d(t)=v(t)

In simple terms, You could say that any change in current makes a voltage across the inductor.
In DC, there is no change in current, just a flat line. No change in current, no voltage...hence your closed or short circuit once again.

Works the same but opposite for Capacitors.
Impedance is 1/(jwc)

Impedance changes with frequency again.
Again, if w=0 you will have a infinite resistance...or open circuit.

C*dv/dt=it

Again, change in voltage induces current. In DC, no change in voltage, no current, open circuit...

Also important to note that the "j" in the impedance, shifts the current out of phase with voltage. If it is purely inductive circuit, the current will shift 90 degrees with a vector pointing down. If it is purely capacitive, it will be a current vector pointing straight up. Ussually tho, there is a combination between real and imaginary current...leading to a current angle somewhere between 0 and 90 degrees. The two derivatives above will accomplish the same thing.

One more, the AC voltage in a receptacle has a frequency of 60 hz. So the current changes directions 60 times per second. So when it hits that coil of wire, an electrical field is induced, but then it changes direction inducing the field the other way...over and over. Same for the capacitor, it starts to charge in one direction, then current changes direction inducing the charge the other way...over and over.
 
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  • #5
The impedance of a[STRIKE] capacitor[/STRIKE] inductor is JWL

i do that all the time too.
 
  • #6
jim hardy said:
The impedance of a[STRIKE] capacitor[/STRIKE] inductor is JWL

i do that all the time too.

True that!
 
  • #7
Another alternative way to look at it:
The essence of an Inductor is that, when you pass a current through it, it has a magnetic field around it (this is true even for a 'wire' only it is more for many turns of wire and particularly if there's a magnetic 'core' inside it). Building up the field involves Energy and this energy is 'stored' in a dynamic way, by the Inductor. This Magnetic energy is analogous to Kinetic Energy of a moving mass. Along with this Energy, there is an electromagnetic equivalent to equivalent to the Mass. Applying an AC voltage across an inductor is the equivalent to trying to 'wobble' a massive object. The faster the wobble (higher the AC frequency) and the bigger the mass (Inductance), the smaller the displacements of the wobble (Currents flowing in the Inductor for a given applied voltage).
 
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1. What is an inductor?

An inductor is a passive electronic component that stores energy in the form of a magnetic field. It is typically made of a coil of wire and is commonly used in electronic circuits to control the flow of electricity.

2. Why doesn't an inductor act as a closed circuit to AC?

An inductor does not act as a closed circuit to AC because of its inherent property of inductance. When an alternating current passes through an inductor, it creates a changing magnetic field around the coil. This changing magnetic field induces a voltage in the inductor, which opposes the current flow. As a result, the inductor impedes the flow of alternating current, preventing it from acting as a closed circuit.

3. How does an inductor behave in a DC circuit?

In a DC circuit, an inductor behaves like a short circuit. This is because in a DC circuit, the current is constant and does not change direction. As a result, there is no changing magnetic field created in the inductor, and hence there is no induced voltage to oppose the current flow. Therefore, the inductor behaves like a wire with very low resistance.

4. What is the role of inductors in AC circuits?

The primary role of inductors in AC circuits is to control the flow of current and voltage. They are commonly used in filters, oscillators, and transformers. They can also be used to store energy and create a phase shift in AC circuits.

5. How is the behavior of an inductor represented in a circuit diagram?

An inductor is represented in a circuit diagram with the symbol of a coil. The coil has two parallel lines and a curved line connecting them, representing the winding of wire. The direction of the curved line indicates the direction of the current flow in the inductor. The value of the inductance is also specified next to the symbol, usually in units of Henry (H).

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