In a circuit, an inductor opposes changes in current by creating a voltage across it proportionate to the rate of change of the current. A sinusoidal voltage is produced when an alternating current (AC) passes through an inductor. The frequency at which this occurs is called the inductor's resonant frequency. At and around this frequency, the inductor will store energy more efficiently than at other frequencies.
Inductors can also affect current by changing its direction. This is usually done with magnetic components such as transformers and inductors. Inductive loads include electric motors, solenoids, and generators. An inductor will try to restore its original shape once the force causing it to change shape has been removed. So, when current is allowed to flow through an inductor again, it will do so in the same direction as before, restoring power lossing circuits.
Inductance is a measure of a component's ability to store energy in a magnetic field. It is expressed in henries (H), which is the SI unit for inductance, or in milliohms (mho). For example, a typical household light bulb has an impedance of about 150 ohms, which means that it will draw about 1.5 amperes from a source such as a battery.
An inductor serves as a conductor in a direct current circuit. Current leads voltage by 90 degrees in an alternating current circuit. Current lags voltage by 90 degrees in an alternating current circuit. A capacitor does not lead or lag current.
Inductors create an opposing voltage proportionate to the rate of change in current in a circuit as a result of the magnetic field associated with the current flow. Inductance is induced by the magnetic field created by an electric current passing through a circuit. The more rapidly the current changes, the greater the inductive reactance.
As current increases so does the inductive reactance, thereby limiting the rate of change of current. As a result, less voltage is available across the terminals of the inductor and more energy is stored in the magnetic field surrounding the inductor coil.
This increased magnetic field also causes more current to be drawn from any source connected to the inductor. This reduces the amount of current flowing into the inductor from such a source and increases the amount of current flowing out of it. In other words, inductance acts like a load on the source providing current to the inductor.
As current decreases so does the inductive reactance, thereby allowing the rate of change of current to increase again. When current reaches zero, the inductor's magnetic field collapses and its inductive reactance goes to zero. At this point, there is no opposition to the flow of current into or out of the inductor and its resistance returns to zero energy is not stored in the magnetic field and the current flows freely back into its source.
Inductors resist changes in current flow in the same way as capacitors resist changes in voltage. When an inductor is connected to the circuit, the current rapidly increases, but the growing magnetic field obstructs the current. This causes more delay than when connecting a capacitor, so much time has passed before the current decreases that the magnetic field has had enough time to grow strong enough to prevent further increase in current.
Inductors have two main types: self-inductance and mutual inductance. Self-inductance is the tendency of a single coil to create a magnetic field around itself. Mutual inductance is the effect that one coil's magnetic field has on another nearby coil.
Inductors can be used in circuits to limit the rate of change of current or voltage. For example, an inductor can be used in conjunction with a resistor to make a slow-acting switch for use in pulsing power supplies or electromagnets. Inductors can also be used to filter high-frequency noise from power lines or microchips.
Inductors come in many forms including coils of wire, metal plates, and semiconductor devices such as transistors and diodes. They are important components in many circuits such as radio receivers, televisions, and microwave ovens to name just a few.
When current is going to flow through the inductor, the magnetic field created by that current cuts across the other windings, producing an induced voltage and preventing any changes in the current level. The inductor does not let AC current to travel through it, but it does permit DC current to flow through it. This type of circuit is called a "current-loop" because the current flows through both the primary and secondary circuits of the transformer.
The inductor will draw some amount of current even when no power is being delivered to it. This is known as its "standby current". The smaller the value of this current, the less power it will use when nothing is being done to keep it activated. For example, if the standby current of an inductor is 1 mA, then even when shut off, it will still consume energy - so long as it remains plugged in. But if the standby current is 0.1 mA, then it will all be used up when the device is turned off.
Inductors can get very hot when current is flowing through them. The amount of heat they produce depends on how much current they are getting shot with. Inductors work by storing energy in their magnetic field, which can then be released later when needed. This process requires some amount of power to maintain the magnetic field, which increases the temperature of the inductor.
A perfect inductor would have 0% resistance to a steady direct current. Only superconducting inductors, on the other hand, have true zero electrical resistance. Real inductors have some resistance, but this is very small compared to their conductors (wires) and should be negligible for all practical purposes.
An inductor can be thought of as a coil of wire with many turns. Current flows into one end of the coil, around its entire perimeter, back out the other end. The more turns there are on the coil, the higher the inductance value will be; also, the larger the cross-sectional area of the conductor, the greater the current it can carry.
Inductors are used in circuits to limit the flow of current through a line or cable during transmission changes or when a load requires a constant current rather than a constant voltage. This is important when transmitting data over long distances, because otherwise the current would need to be kept high enough to keep the signal strong yet not so high as to damage the wiring. An inductor uses magnetic fields to store energy while allowing current to pass through it.