Inductance; and transformers
Explain the relationship between the magnetic field and the electromotive force . in magnetic flux depends on the change in flux Δ, time Δt, and number of turns of It is the fundamental operating principle of transformers, inductors, and many . Faraday's law tells us that a changing magnetic flux will induce an emf in a coil. including the area and number of turns in coil 2, the distance between the two What's far more important in the equation above is that the emf. Experiments with magnets and our surroundings a. Links for this topic N is the number of turns of wire seeing the changing magnetic field iii. dΦ is the.
One way to use it is in a transformer, which we'll discuss below. Another is to use it in an ammeter. Conventional ammeters are incorporated directly into circuits, but ammeters don't have to be placed in the current path for alternating current.Transformers Physics Problems - Voltage, Current & Power Calculations - Electromagnetic Induction
If a loop connected to a meter is placed around a wire with an AC current in it, an emf will be induced in the loop because of the changing field from the wire, and that will produce a current in the loop, and meter, proportional to the current in the wire.
Self inductance Coils can also induce emf's in themselves. If a changing current is passed through a coil, a changing magnetic field will be produced, inducing an emf in the coil. Again, this emf is given by: As with mutual inductance, the induced emf is proportional to the change in current. The induced emf can be written as: The constant L is known as the inductance of the coil. It depends on the coil geometry, as well as on whether the coil has a core of ferromagnetic material.
We've already discussed resistors and capacitors as circuit elements. Inductors, which are simply wire coils, often with ferromagnetic cores, are another kind of circuit element. One of the main differences between these is what happens to electrical energy in them. Resistors dissipate electrical energy in the form of heat; capacitors store the energy in an electric field between the capacitor plates; and inductors store the energy in the magnetic field in the coil. The energy stored in an inductor is: In general, the energy density energy per unit volume in a magnetic field is: Transformers Electricity is often generated a long way from where it is used, and is transmitted long distances through power lines.
This current produces a flux field about the secondary shown as broken lines which is in opposition to the flux field about the primary Lenz's law. Thus, the flux about the secondary cancels some of the flux about the primary.
With less flux surrounding the primary, the counter emf is reduced and more current is drawn from the source.
The additional current in the primary generates more lines of flux, nearly reestablishing the original number of total flux lines. The ampere-turn I X N is a measure of magneto motive force; it is defined as the magnetomotive force developed by one ampere of current flowing in a coil of one turn. The flux which exists in the core of a transformer surrounds both the primary and secondary windings.
Since the flux is the same for both windings, the ampere-turns in both the primary and secondary windings must be the same. By dividing both sides of the equation by IpN s, you obtain: Notice the equations show the current ratio to be the inverse of the turns ratio and the voltage ratio. This means, a transformer having less turns in the secondary than in the primary would step down the voltage, but would step up the current. A transformer has a 6: Find the current in the secondary if the current in the primary is milliamperes.
The above example points out that although the voltage across the secondary is one-sixth the voltage across the primary, the current in the secondary is six times the current in the primary. The above equations can be looked at from another point of view. The turns ratio indicates the amount by which the transformer increases or decreases the voltage applied to the primary.
For example, if the secondary of a transformer has two times as many turns as the primary, the voltage induced into the secondary will be two times the voltage across the primary. If the secondary has one-half as many turns as the primary, the voltage across the secondary will be one-half the voltage across the primary. However, the turns ratio and the current ratio of a transformer have an inverse relationship.
A transformer with a turns ratio of 1: Magnetic field strength the magnetic flux density.
Number of pieces of wire. These factors inform many modern designs- motors, generators and dynamos all have many turns of wire inside them. We have created an induced current and therefore a voltage must exist across the wire. This voltage is driving the current and is therefore an electromotive force EMF.
BBC - Intermediate 2 Bitesize Physics - Electromagnetism : Revision, Page 2
Faraday's Law The induced electromotive force across a conductor is equal to the rate at which magnetic flux is cut by the conductor. We can deduce the equation for this induced EMF Considering a long straight wire cutting a magnetic field perpendicularly to the field lines.
The force acing on the wire is given by Electrical energy is given by emf x charge This is the magnetic field cut by a wire of length l, moving a distance x, in a magnetic field B.