The phenomenon in which electric current is generated by varying magnetic fields is appropriately called electromagnetic induction.
The discovery and understanding of electromagnetic induction are based on a long series of experiments carried out by Faraday and Henry.
In the first experiment of Faraday and Henry, a coil was connected to a galvanometer. Then a bar magnet was pushed towards the coil. This was done in a way that the north pole was pointing towards the coil. It was noticed that as the bar magnet shifted, the galvanometer showcased deflection. The same thing was done with the south pole.
It was observed in this experiment of Faraday and Henry that the shift and deflection took place only when the magnet was in motion and not when it was stationary. The point of deflection is small or large depending on the speed at which the motion takes place.
The conclusion of the Faraday and Henry experiment was that there was relative motion between the coil and magnet resulting in the generation of current in the coil.
In this experiment, the bar magnet of the circuit was replaced with another coil that had current generated within it that was connected to a battery. The current coil which was connected to a battery produces a steady current. The second coil that was the primary coil shows deflection in the galvanometer pointer which indicates the presence of current in it.
Here, same as above, the degree to which the deflection took place depended on the motion of the secondary coil towards the primary coil. The magnitude also depends on the speed with which it was moved. This shows how the second case is analogous to the first.
The third experiment of Faraday and Henry showcases that the relative motion is not necessary to produce current. Both of the coils are steadily placed, one is connected to the battery and the other to a galvanometer. The button in the battery when pushed repeatedly does not pass current but when pushed once, the galvanometer deflects.
Hopefully, some concepts of the experiment by Faraday and Henry are clear.
Magnetic flux is defined as the number of magnetic field lines passing through a given closed surface. It provides the measurement of the total magnetic field that passes through a given surface area. Here, the area under consideration can be of any size and under any orientation with respect to the direction of the magnetic field.
Magnetic flux is usually measured with a flux meter. The SI and CGS unit of magnetic flux is given below:
Faraday’s law of electromagnetic induction, also known as Faraday’s law is the basic law of electromagnetism which helps us to predict how a magnetic field would interact with an electric circuit to produce an electromotive force (EMF). This phenomenon is known as electromagnetic induction.
The law was proposed in the year 1831 by an experimental physicist and chemist named Michael Faraday. So you can see where the name of the law comes from. That being said, the Faraday’s law or the law of electromagnetic induction is basically the results or the observations of the experiments that Faraday conducted. He performed three main experiments to discover the phenomenon of electromagnetic induction.
In 1834, German physicist Heinrich Friedrich Lenz (1804-1865) deduced a rule, known as Lenz’s law which gives the polarity of the induced emf in a clear and concise fashion. The statement of the law is “The polarity of induced emf is such that it tends to produce a current which opposes the change in magnetic flux that produced it”
A magnet moved toward a coil induces an emf, and a coil moved toward a magnet produces a similar emf. In this section, we concentrate on motion in a magnetic field that is stationary relative to the Earth, producing what is loosely called motional emf.
One situation where motional emf occurs is known as the Hall effect and has already been examined. Charges moving in a magnetic field experience the magnetic force F = qvB sin θ, which moves opposite charges in opposite directions and produces an em f = Bℓv.
Force is the push or pull of an object and performing a day-to-day task we apply force on our bodies. For exerting our body, we need energy. So, here can find a link between the force and the energy. Also, the thing that provides a link between these two quantities is the energy consideration.
Through the concept of energy consideration in motional emf, we can prove that motional emf is correct or valid according to the conservation of energy.
Eddy currents are currents which circulate in conductors like swirling eddies in a stream. They are induced by changing magnetic fields and flow in closed loops, perpendicular to the plane of the magnetic field.
Eddy currents are used to advantage in certain applications like:
(i) Magnetic braking in trains: Strong electromagnets are situated above the rails in some electrically powered trains.
(ii) Electromagnetic damping: Certain galvanometers have a fixed core made of nonmagnetic metallic material.
(iii) Induction furnace: Induction furnace can be used to produce high temperatures and can be utilised to prepare alloys, by melting the constituent metals.
(iv) Electric power meters: The shiny metal disc in the electric power meter (analogue type) rotates due to the eddy currents.
Inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. The flow of electric current creates a magnetic field around the conductor.
Inductance is a scalar quantity. It has the dimensions of [M L 2 T –2 A –2] given by the dimensions of flux divided by the dimensions of current. The SI unit of inductance is henry and is denoted by H. It is named in honour of Joseph Henry who discovered electromagnetic induction in USA, independently of Faraday in England.
Mutual inductance is the main operating principle of generators, motors, and transformers. Any electrical device having components that tend to interact with another magnetic field also follows the same principle. The interaction is usually brought about by a mutual induction where the current flowing in one coil generates a voltage in a secondary coil.
Self inductance is an effect that is noticed when a single coil experiences the effect of inductance. Under the effects of self inductance and changes in current induce an EMF or electro-motive force in that same wire or coil, producing what is often termed a back-EMF.
An alternating current (AC) generator is a device that produces a potential difference . A simple ac generator consists of a coil of wire rotating in a magnetic field. Cars use a type of ac generator called an alternator to keep the battery charged and to run the electrical system while the engine is working.
Disadvantages of ac generators:
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