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The SI unit of electrical inductance is the Henry, abbreviated as H and defined as 1 kg⋅m2⋅s−2⋅A−2. The unit is named after Joseph Henry, the American scientist who discovered electromagnetic induction at about the same time as Michael Faraday in England. The Henry is a large unit and is less frequently used than smaller units like millihenry (mH) or micro-Henry, which are used to measure radio frequency and audio-frequency ranges. The SI unit of self-inductance can also be expressed as Weber/Ampere, Volt second/Ampere, Joule/Ampere square, or Ohm second.
| Characteristics | Values |
|---|---|
| SI unit of electrical inductance | Henry (H) |
| Symbol | H |
| Definition | 1 kg⋅m2⋅s−2⋅A−2 |
| Alternative units | Weber/Ampere, Volt second/Ampere, Joule/Ampere square, Ohm second |
| Smaller units | Millihenry (mH), Micro-Henry, Nano-Henry |
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What You'll Learn
The Henry (H)
The Henry, with the symbol H, is the unit of electrical inductance in the International System of Units (SI). It is defined as 1 kg⋅m2⋅s−2⋅A−2.
The unit is named after Joseph Henry (1797–1878), an American scientist who discovered electromagnetic induction independently and at the same time as Michael Faraday (1791–1867) in England.
A coil has a self-inductance of 1 Henry when a current of 1 ampere flowing through it produces flux linkage of 1 weber turn. The inductance of an electric circuit is one henry when an electric current that is changing at one ampere per second results in an electromotive force of one volt across the inductor.
An inductor is a coil of wire wrapped around a magnetic material. As the current in the coil changes, the surrounding magnetic field also changes. This change in the magnetic field can cause the coil to generate electromotive energy. The larger the inductance of the inductor, the slower the current will decay. The inductance of a circuit depends on the number of wires transforming into a coil, the material of the coil, and the length of the coil.
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Inductors and their function
Inductors, also known as coils, chokes, or reactors, are passive two-terminal electrical components that play a crucial role in various electrical applications. They are designed to store energy in a magnetic field when an electric current flows through them. The core principle behind inductors is inductance, which is the tendency of an electrical conductor to resist changes in the electric current passing through it.
At its most basic, an inductor consists of an insulated wire wound into a coil. When an electric current passes through the coil, it generates a magnetic field. According to Faraday's law of induction, any variation in this magnetic field results in the production of electromotive force (EMF), often represented by the voltage across the coil. This phenomenon is described as self-inductance. The induced voltage, governed by Lenz's law, has a polarity that opposes the change in the current, leading to the stabilisation of the current flow within the inductor.
The unit of measurement for electrical inductance in the International System of Units (SI) is the henry (H), named after 19th-century American scientist Joseph Henry. One henry is defined as the amount of inductance that results in an electromotive force of one volt when an electric current changes at a rate of one ampere per second. Mathematically, this can be expressed as 1 H = 1 kg⋅m2⋅s−2⋅A−2.
The unique behaviour of inductors makes them valuable in a variety of applications. They are commonly used in power sources to convert alternating current (AC) to direct current (DC) by choking the AC current flow while allowing DC to pass through. This property is also utilised in computer parts and charging cables to reduce radio interference. Inductors are essential in radio tuning circuits, where they facilitate frequency modification and channel selection. Additionally, inductors find use in traffic lights, where they power the inductive proximity sensors used to detect traffic density.
The design of an inductor can vary, with some featuring a moveable ferrite magnetic core that can be adjusted to increase or decrease the inductance. This adjustability is particularly useful in radio applications, where tuning is required. Another type of inductor is the variometer, which consists of two coils connected in series, one inside the other. By changing the relative orientation of the coils, the overall inductance can be varied over a wide range, making variometers useful in antenna tuners and matching circuits.
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How inductance is calculated
The SI unit of electrical inductance is the henry, with the symbol H. It is defined as 1 kg⋅m2⋅s−2⋅A−2. One henry is equal to one weber turn when a current of one ampere is flowing through a coil.
Inductance is the property of a component that opposes the change of current flowing through it. Inductance is calculated using the formula L = R * sqrt(3) / (2 * pi * f), where L is the inductance, R is the resistance, and f is the frequency. This formula can be used to calculate the inductance of a coil, which is an example of self-inductance.
Self-inductance occurs when a current flows into a coil, producing a magnetic field around it. The inductance of a coil is proportional to the number of turns squared (N^2). This is because the more turns in a coil, the stronger the magnetic flux for a given value of the current, resulting in higher inductance.
To measure inductance, a function generator and an oscilloscope can be wired into a circuit. The function generator simulates currents and allows control over the signal moving through the coil, while the oscilloscope displays the input and resistor voltages. By monitoring these values and calculating the junction voltage and frequency, the inductance can be determined using the formula mentioned above.
Another formula for calculating inductance is L = V*Ton/Ipk, where V is the voltage delivered by the pulses, Ton is the time between each pulse, and Ipk is the peak current. This formula demonstrates the relationship between voltage, time, and current in determining the inductance of a circuit.
It is important to note that inductance is independent of the current and depends on the magnetic permeability of the material. The size, material, and length of the coil also influence the inductance, with shorter coils generally exhibiting higher inductance.
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The relationship between electric current and magnetic fields
The unit of electrical inductance in the International System of Units (SI) is the henry, with the symbol H and defined as 1 kg⋅m2⋅s−2⋅A−2. The unit is named after Joseph Henry, the American scientist who discovered electromagnetic induction.
Now, let's discuss the relationship between electric current and magnetic fields. Electric currents and magnetic fields are fundamentally connected, a phenomenon known as electromagnetism, which is a cornerstone of modern physics. This relationship is described by Maxwell's equations. When an electric current flows through a wire, it generates a circular magnetic field around that wire. The strength of this magnetic field depends on the amount of current flowing.
This principle works in reverse as well: moving a magnet near a wire can induce an electric current. This reciprocal relationship is the basis for many electrical devices, including electromagnets, electric motors, generators, and transformers.
The direction of the magnetic force on a moving charge is perpendicular to the plane formed by the direction of the moving charge and the magnetic field. This can be determined using the right-hand rule, where the thumb points in the direction of the moving charge, the fingers in the direction of the magnetic field, and a perpendicular palm points in the direction of the magnetic force.
The magnetic effect of electric current refers to the creation of a magnetic field around a current-carrying conductor. This effect is influenced by factors such as the number of turns in the coil, the magnetic permeability of the material, and the cross-sectional area. The inductance of a coil or inductor can impact the rate of current decay, with larger inductance resulting in slower current decay.
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The discovery of inductance
The SI unit of electrical inductance is the henry, which is defined as 1 kg⋅m2⋅s−2⋅A−2. The unit is named after Joseph Henry, an American scientist who discovered electromagnetic induction independently of and concurrently with Michael Faraday in England.
Michael Faraday is generally credited with discovering electromagnetic induction in 1831, and James Clerk Maxwell mathematically described it as Faraday's law of induction. Faraday's law states that any variation in the magnetic field generates electromotive force (EMF). The negative sign in the equation indicates that the induced voltage opposes the change in current, which is known as Lenz's law.
In Faraday's first experiment, he wrapped two wires around opposite sides of an iron ring. He observed a transient current, which he termed a "wave of electricity," when he connected and disconnected the wire from a battery. Within two months, Faraday discovered several other manifestations of electromagnetic induction. For example, he observed transient currents when quickly sliding a bar magnet in and out of a coil of wires, and he produced a steady (DC) current by rotating a copper disk near a bar magnet with a sliding electrical lead ("Faraday's disk").
Joseph Henry, an American physicist and inventor, also discovered electromagnetic induction independently of Faraday around the same time. Henry did not publish his work and was not credited as the discoverer. In 1831, Henry created one of the first machines to use electromagnetism for motion, which was the earliest predecessor of the modern DC motor. He also invented a precursor to the electric doorbell and the electric relay.
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Frequently asked questions
The SI unit for electrical inductance is the Henry, abbreviated as H.
The unit was named after Joseph Henry (1797-1878), the American scientist who discovered electromagnetic induction.
One Henry is defined as 1 kg⋅m2⋅s−2⋅A−2. In practical terms, it is the amount of inductance that causes a voltage of one volt when the current is changing at a rate of one ampere per second.
Yes, smaller units such as millihenry (mH) or micro-Henry are used to measure radio and audio-frequency ranges. The nano-Henry unit is used for very high-frequency ranges.
