This is used to adjust frequencies in radio circuits. By moving the core in and out of the coil, the effective permeability of the coil can be varied and so, the inductance of the coil. These inductors are easiest to construct.Ī solenoidal or cylindrical coil can be easily designed to vary inductance by incorporating a mechanism to slide in and out ferromagnetic core of the coil. These inductors are cylindrical coils wound around air-core or ferromagnetic core. The simplest and most common inductors are solenoidal coils. Commonly, solenoids are used as electromagnets in electric bells, DC motors, and relays.
The solenoids are specifically used as electromagnets and usually have a moveable or static core. Though, they are not intended to be used as an electromagnet in a circuit. The inductors using cylindrical coils are also called solenoidal coils only because of their solenoid like construction. Many inductors are also coils of wires but they are intended to offer inductance in a circuit. The solenoids are coils of wires that are intended to be used as electromagnets. Solenoids are often confused with the inductors. At high currents, the ferromagnetic cores may get enough hot that they may fracture and permanently change the nominal inductance of the inductor. On increasing current beyond critical value, the inductance may, instead, starts decreasing. With ferromagnetic cores, the inductance is saturated at a critical value of current. The use of ferromagnetic cores also limits the current-carrying capacity of the inductor. However, the powdered iron or ferrite core also has a significant loss of electrical energy in the form of heat. So, air-core inductors are quite suitable for high-frequency AC circuits due to lossless operation, high current capacity and sufficient inductance values.īy using powered iron or ferrite cores, the inductance can be significantly increased. Higher is the frequency of AC current, less is the inductance required to produce significant effects. These inductors are almost lossless as air does not dissipate much energy in the form of heat. The air-core coils can be designed to have unlimited current-carrying capacity by using heavy-gauge wire over a large radius. The air-core coils offer small inductances that can be a maximum 1 mH. The operating losses (in the form of heat) from an inductor largely depend on the material used as a core in the inductor.Įxample of air core inductor (Image: Wurth Electronics) The current carrying capacity of the inductor depends upon the material and thickness of the wire. So, closer will be the turns, greater will be the inductance. It is inversely proportional to the length of the wire for a given diameter and number of turns of the coil. The inductance is proportional to the number of turns as well as the diameter of the coil. The inductance of a coil depends upon the number of turns, radius of the coil and overall shape of the coil. These are constructed by winding a coil of wire around plastic, wood or any non-ferromagnetic core. The simplest inductors are air-core coils. The inductance of a loop or coil of wire can be multiplied many times by using a suitable ferromagnetic core. More the number of loops for the same length of wire, greater the inductance is shown by it. If the same wire is wrapped in a loop, its inductance is increased.
Even a simple straight wire shows some inductance, though it is small enough to be neglected in a circuit. Any conductor shows some inductance in response to change in magnitude or direction of the current. Most of the conducting materials (metals) are paramagnetic or ferromagnetic while most of the non-conducting materials (non-metals) are diamagnetic. The electronic components that are designed to offer inductance in a circuit are called inductors. In the previous tutorial, we discussed magnetism, electromagnetism and inductance.