Inductive coupling is when a magnetic field from an electric current induces an effect on something else, creating a mutually reactive relationship. It is used in transformers, electric motors, and resonant devices to create desired electric currents, mechanical effects, or resonance. Transformers use induction to connect two circuits without physical contact, while motors use induction to create a mechanical force. Resonant devices create a permanent electromagnetic field that induces an electric current in an antenna, which can be amplified in radios or used to recharge batteries.
Inductive coupling refers to the phenomenon that exists when a magnetic field created by an electric current induces an effect on something else. When this happens, the two then become mutually reactive, or coupled, due to the inductive effects of the magnetic field. For example, when an electric current passes through one wire, the electromagnetic field created can induce an electric current in another wire, causing the two to couple inductively. The principles and effects of inductive coupling find use in devices such as transformers and electric motors.
The effects of inductive coupling can be used in one of three main ways. First, the inductor field can create a specifically desired electric current, as in transformers. Second, the inducing field can create a specifically desired mechanical effect, such as in electric motors. Finally, the inductive field can create a resonance, which in turn can create specifically desired electric currents, such as in radio transmission and reception and non-contact charging devices.
In transformers, an electric current conducts through a wire wound around a core of some sort, called the primary winding. This wire is intentionally placed near another wire wound around the same core, called the secondary winding. The electromagnetic field, created by passing current through the primary winding, then induces an electric current in the secondary winding.
If the two windings have the same number of turns around the core, it allows the primary winding to pass an exact replica of its electric current to the secondary winding. These types of transformers are generally called isolation transformers. Through induction, they allow two circuits to be connected or electrically coupled, without actually coming into direct physical contact, which physically isolates the two circuits from each other.
When the primary and secondary windings do not have the same number of turns around the core, inductive coupling causes a different effect. The electromagnetic field created by the primary winding will induce a current of value proportional to the difference between the two windings. For example, if the primary winding is 10 turns around the core and the secondary winding is 20 turns around the core, the current induced in the secondary winding will be twice the voltage of the current flowing through the primary winding.
An electric motor uses a different aspect of the electromagnetic field. In a simple motor, a wire is wound around a rotor which forms the rotating shaft of the motor. When an electric current is passed through the wire, it creates an electromagnetic field. This field then induces a mechanical force by moving away and pulling towards the magnets mounted around the rotor, depending on the polarity of the magnetic fields.
Resonant devices work similar to transformers, however, without the coupled windings. A permanent electromagnetic field is created in these devices. When this field encounters an antenna, the effect of inductive coupling causes the antenna to resonate, which in turn induces an electric current at its feed point. In the case of a radio, the induced current is amplified and listened to via the radio. In a charging device, induced current is applied directly to the terminals of a battery to recharge it.
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