Electromagnetic Induction - Laws of Electromagnetic Induction - Applications of Electromagnetic Induction - Working Principle of Electromagnetic Induction - Faraday's Law of Electromagnetic Induction - Electromotive Force - Motional EMF - Production of Electromagnetic Induction
Electromagnetic Induction
Every electrical machine works on electromagnetic
induction which produces energy and the machine starts
running. Every electrical machine requires the Electromotive Force
(EMF) in it to start running. Our electricity generation from hydroelectric
power plants, nuclear power plants, steam power plants, oil
fired plants, coal power plants etc. produce electrical energy with
the process known as electromagnetic induction.
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| Electromagnetic Induction |
Electromagnetic induction is a process in which the changing/variable magnetic flux is produced in a circuit or in a conductor then an EMF/current is induced in that circuit or in a conductor. This phenomenon of EMF induction is known as electromagnetic induction. The working principle of electromagnetic induction is Faraday’s law of electromagnetic induction.
The Faradays Law of Electromagnetic Induction
tells us about the changing magnetic flux in a loop and Lenz’s law indicates
the direction of the induced emf and current. The magnetic field acts as
a source of electric field and the electric field acts as a source of a
magnetic field in the process of electromagnetic induction. This drives from Maxwell’s
Equation. These equations also teach us about electromagnetic waves.
Experimentations of Electromagnetic Induction
The first process of Electromagnetic Induction was practically proved by Michael Faraday in
1830 in England. The second practical of electromagnetic induction was
performed by Joseph Henry in 1877 or in 1878 in United States. Figure
(a) shows that a coil of a conductor is connected to the Galvanometer
and a stationary magnet is placed near to the coil and the galvanometer
remains on the zero position. While in figure (b) if we move the magnet in
upward and downward direct to the coil, the galvanometer shows a current this
current is known as induced current. In figure (c) we replace the magnet to the
second coil and make the second coil stationary then no current is produced in
it but if we move the second coil in upward and downward direction then the current
will start flowing in the first coil.
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| Process of Electromagnetic Induction |
In
figure (d) both the coils are stationary and we have a single way switch
connected to the supply and to the first coil. The second coil is not connected
to any supply except the galvanometer to check the induced current in it. We
will check by turning on and off the single way switch continuously and you will notice that a minor
current is producing in the second coil. This produced current is in a form of
pulse and it is the induced current in the circuit if the supply current of the
first coil is changing continuously. Otherwise no current will produce in the
second coil. By experimenting all the things, we observed the following key
points:
- If there is no current in the electromagnet, the magnetic flux is zero so the galvanometer cannot show any current on its scale.
- If the electromagnet has some current, the flux is produced in it so the galvanometer will show a minor current on its scale.
- If the magnetic flux remains steady in some value the no current will be produced in the coil.
For
further let’s discuss about induced EMF:
Electromotive
Force (EMF)
Electromotive Force (EMF) is a current produced in conductor through the magnetic field. EMF is the energy per unit area and its SI unit is volt which is equal to one joule per coulomb. If a battery or a DC source which has 3 volts then it means that it has 3 joules of work on each coulomb of charge. EMF is denoted by ε.
EMF works
on the principle of Faraday's Law of Electromagnetic Induction which
states that ‘When a moving conductor is placed between a magnetic
field, A force is produced in the conductor named as Electromotive Force
(EMF)”. EMF is also known as no load voltage/ on load voltage which
is the force to move electrons in any cross-sectional area/conductor and it
helps to flow the current in the conductor. Let's read about Faraday's law of
electromagnetic induction.
Faraday’s Law of Electromagnetic Induction
Faraday’s Law of Electromagnetic Induction is about magnetic field and it proves that an EMF is produced in a moving conductor when placed it in a magnetic field. Faraday’s law of electromagnetic induction is further divided into two laws:
Faraday’s First Law of Electromagnetic Induction
Faraday’s First Law of Electromagnetic Induction states that “When a conductor cuts a magnetic flux, an EMF is induced in that conductor.” A Simple loop generator/loop generator is based on this law of Electromagnetic Induction.
Faraday’s law is denoted by ε and its formula is:
The above formula is also known as faraday’s law of induction. In
the above formula,
Faraday’s Second Law of
Electromagnetic Induction
Faraday’s Second Law of Electromagnetic Induction states that “The
magnitude of generated EMF in a conductor (wire) is equal to the rate of change
of flux linkage.”
The conversion of mechanical energy into electrical energy is
based on the faraday’s first law of electromagnetic induction and this law is
used in the construction of DC Generator. Without this law, DC Generator
is not capable to convert mechanical energy to DC Electrical Energy.
Production of EMF
As shown in figure that a coil is connected across the Galvanometer and a stationary magnet is placed in space and when we move the stationary magnet inside the coil and we move the stationary magnet inward and outward between the coil so the deflection is produced in galvanometer scale. This deflection states that an EMF is produced in the coil when we move inward and outward between the coil continuously.
In this process, A magnetic field is produced across a coil due to
the movement of the coil and due to the magnetic field and the continuous
movement of a magnet, a force is produced named as electromotive force (emf)
through which the current flows in a coil and the deflection is occurred on the
scale of the galvanometer. The amount of the current is
minor so that the deflection of the galvanometer is steady and it indicates the
sensitive current on its scale. If we increase the material and more space is
available then we can produce large amount of current in a coil. It all depends
on the size of the material and its quality.
Direction of Induced EMF and the Current Produced in a Coil
The direction of the induced current is found by smearing the Fleming right hand rule, Fleming flat hand rule and by Lenz’s law.
Fleming’s Right-Hand Rule
These rules are used on those places where magnetic flux is cutting
with any other force and where flux linkage is occurred. The figure below
indicates that how Fleming’s Right-Hand Rule works and how to use
Fleming right hand rule. This rule is used to measure the direction of EMF in a
conductor. In the Fleming right hand rule, the thumb indicates the motion of
the conductor, the first finger indicates the direction of magnetic field and
the second finger indicates the direction of EMF.
Fleming’s Flat Hand Rule
In the process of Fleming flat hand rule, A right hand is used to
indicate the direction of the current and the EMF. This rule is used to measure
the direction of EMF in a conductor. In this rule, the flat right hand is held
perpendicular between the magnet bars and thumb shows the direction of motion
of the conductor and the other fingers shows the direction of the induced EMF.
Both methods are very easy and you can implement these methods very easily.
Lenz’s Law
Lenz’s Law states that “The effect produced always
opposes the cause by which the effect is produced”. By Lenz’s law we can
measure the direction of induced emf in a coil. The figure below shows the coil
and a magnet and when we insert the north pole of the magnet inside the coil
the electric current is produced in it due to the induced EMF and the current
moves in anti-clockwise direction and the coils become north pole and attracts
the bar magnet. If we insert the south pole of the bar magnet inside the coil
then the current flows in clockwise direction and the coil becomes south pole
and repels the bar magnet.
Types of Induced EMF
The EMF induced in a circuit or loop consist of
two Types/methods either dynamically and statically induced EMF. Dynamically induced
EMF is used in DC Generators and the statically induced EMF is used in transformers.
Dynamically Induced EMF
Dynamically Induced EMF is defined as “The emf
induced in a coil due to relative motion of the conductor and the magnetic
field”. In this case, the magnetic field is fixed and the conductor moves and
cuts the flux so that the EMF is produced. DC generator works on the principle of
dynamically induced emf.
Statically
Induced EMF
Statically Induced EMF is defined as “The emf induced in a coil due
to change of flux linked with it is called Statically Induced EMF.”
In this case, the conductor is fixed and the flux changes continuously. Transformer
is an example of statically induced emf. Here the windings are stationary and
the magnetic field is moving around the conductor and produces EMF. Statically
induced EMF is divided into mutually induced EMF and self-induced EMF.
Mutually Induced EMF
In this case of EMF Induction, if we place two coils nearly to
each other and one coil is connected to the supply and the other is not
connected to any source of current and it is connected with the voltmeter only.
When we give the supply to the first coil then it will produce a flux across it
and this flux starts linking to the other coil and as a result an EMF is
produced in the second coil without any electric connection. The EMF is only
produced in the second coil due to the flux linkage. It is also known as Mutual
Inductance.
Self - Induced EMF
In this case, when we change the value of the current in a coil
then the flux linked with the coil is changed and due to changing in flux
linkage of the coil an EMF is produced in it and this EMF is known as Self-Induced
EMF. It is also known as self-inductance.
Production of EMF in Direct Current (DC) Circuit
In dc circuits the emf is gained from the battery and the emf of the battery is defined as the maximum voltage of the battery gained from its terminals. The positive terminal of the battery consists of high potential then the negative terminal. In the figure, the resistance is connected in series with the battery. The battery provides the emf ε and the resistance provides the resistance r. So, the terminal voltage of the battery is equal to:
Where ε are the open circuit voltage and
to calculate the EMF of the circuit
and the current will be equal to
The above equation indicates the current in a DC circuit and it depends on an external resistance and internal resistance.
Measurement
OF EMF
To measure the emf we use a device which is named as Galvanometer. It is a very sensitive device and it measure a minor amount of current. Emf is the amount of current produced in a conductor or a coil. The procedure is given below:
- Connect a coil of wire to the galvanometer.
- Bring the magnet close to the coil.
- If the magnet is held constant on one position no current is flowed through the coil.
- If the magnet is moving continuously near to the conductor or coil the deflection is occurred in the scale of the galvanometer and the reading is shown on the scale of the galvanometer and it means that current is flowing through the coil and EMF is induced in the conductor.
Motional EMF
Motional
emf is the emf induced in any conductor of any shape which is moving in any
magnetic field assuming that the magnetic field at each point does not vary
with time.
ε = -Blv
Assume a straight rod or a conductor is moving perpendicular in direction with a constant velocity and external driving force. The electrons present in a conductor face a force
along the length of the conductor which is
perpendicular to velocity
Due to this force the electrons move to the
lower end of the conductor and added with each other. The electric field
Then the electric field is produced in a conductor so the
potential difference
So, the balancing equation is
If the direction of the motion of the conductor is reversed then the potential difference will also be reversed.
Assume a circuit which consists of a conducting bar of length l is
placed perpendicular along the two parallel rails and these rails are connected
to the resistor in series on the other end. The magnetic field
The area of the circuit is lx where l is the length of the
conducting bar and x is the position of the magnetic bar thus the magnetic flux
through the area is:
By using Faraday’s law, we find the induced motional emf
The magnitude of the Induced Current is:
The applied force Fapp is equal to the magnetic force FB.
The power due to the applied force is
Induced Electric Fields
As we have understood that the EMF is produced in a changing magnetic field on the basis of magnetic forces applied on the conductor but the question is arising here that what is in the conductor that pushes the charges to flow in the conductor?
So, the answer is that:
Take a long and thin solenoid that have
cross sectional area A and has n number of turns of a coil encircled at its
center and the galvanometer G is measuring the current in the loop. A produced
current in a coil which is encircled on the solenoid produces magnetic field
By deserting the magnetic field from the
solenoid and taking the area
When the current of the solenoid changes with respect to time then the magnetic flux also changes and the induced emf according to the Faraday’s law is:
The induced current
So, the magnetic force can’t move the
charges to move around the loop. So, the answer is that an induced electric
field in a conductor or a coil force the charges to move around the conductor.
This force is produced due to the changing magnetic flux in the conductor.
Eddy Current
Eddy currents are the loops of electric current which is
produced in the conductor by changing the magnetic field in the
conductor. Eddy current is also called foucault current. In closed
loops, eddy current flows in it. Eddy current is induced due to
another conductor which is placed near to the conductor in which magnetic flux
is produced by an AC Electromagnet. These conductors can be in coil
shapes and a transformer.
Lenz’s Law Related to Eddy Current
According
to the Lenz’s Law eddy current creates a magnetic field in a
conductor that opposes the change in the magnetic field which is created in it
and then eddy current reacts back on the source of the magnetic field. In
alternating current eddy current is a name of energy loss in a conductor. This is because of
the resistance of the conductor in the way of electric current. To
reduce the energy loss of eddy current requires the usage of laminated cores.
Explanation OF Eddy Current
In AC Circuits, Eddy current produces in a
conductor. When a conductor produce resistance in the way of current, a minor
amount of current produces which starts flowing to the opposite direction of
the current and a large amount of resistance is produced. This
resistance is because of the resistance of the conductor. Eddy current is
produced in electrical circuits which are used in AC circuits such as inductors, transformers, electric
motors, generators and other AC machinery.
Skin Effect
Alternating Current also cause losses in the conductors in the field of transmission and distribution lines. This is because of the alternating current changes its direction and its quantity continuously with respect to time. In transmission and distribution of electric power, the current flows through the edges of the conductor and cannot flows properly in the whole conductor. This current produces an eddy current due to the resistance of the edges of the conductor and can cause high resistance in the conductor.
Maxwell’s Equations of Electromagnetism
Maxwell’s Equations show
us the relationship between the magnetic and electric fields. There are
four types of Maxwell’s equations and all these equations was not discovered by
Maxwell. He just put them together and succeeded to show the importance of all
these 4 equations.
Maxwell’s equations tell us the charges
and electric currents in an empty space. Two of the Maxwell’s equations are of
electric field
The first equation states that the
surface integral of electric field in a closed surface is equal to the charge
enclosed in that surface. This equation is named as Gauss law of electric
fields.
The second equation states that the surface integral of the magnetic field in a closed surface is always zero. This equation is known as Gauss law of magnetic field.
The above Maxwell’s equation tells us
that there is no any source of magnetic field.
The third Maxwell equation is Ampere’s law with displacement current and it states that the conduction current Ic and displacement current acts as the sources of magnetic field.
where
The fourth Maxwell’s Equation is the Faraday’s law and it states that “An electric field is produced in a changing magnetic field”.
In the above equation, the line integral
is not equal to zero and the electric field
where
The electrostatic part is
conservative so the line integral is zero.
Applications of Electromagnetic Induction
Electromagnetic induction is used in ac
generators, dc generators and in electrical transformers. This phenomenon is
used in the working of all these devices and these devices during their
operation. All the applications of electromagnetic induction are explained in
detail below:
In AC Generator
In the working principle of ac generator,
the process named as electromagnetic induction is used. Faraday’s law of electromagnetic induction is about magnetic field
and it proves that an EMF is produced in a moving conductor when placed it in a
magnetic field.
In DC Generator
In dc generator the electromagnetic field
poles produce flux and this flux acts on an armature and an operating torque is
produced due to this flux and the armature starts moving. This whole phenomenon
relates to Faraday’s law of electromagnetic induction.
In Electrical Transformer
Electrical transformer consists of two
winding known as primary and secondary windings. These two winding are not
connected to each other and are separated with some insulated material but
these winding are connected with flux linkage with each other. Here the
Faradays second law of electromagnetic induction applies which states that “The magnitude of generated EMF in a conductor (wire) is equal to
the rate of change of flux linkage.”
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