As the current has magnetic effect, the magnet has the
electric effect also. Many electric tools have been made by using these two
effects. These tools have solved many problems of us, have brought out various
comforts and have developed the standard of our life.
Oersted invented the magnetic effect of current.
Do yourself. Make a circuit like the picture below. Place a
compass under the wire as if it faced to North-South. Now let the switch on.
What is happening to the needle of compass?
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| Magnetic effect of current |
We see that the needle is moving to one side after switching on
the current on circuit. If we alter the electric connection, the needle of the
compass will move the other side. From this effect, we can understand that a
magnetic field is produced when a current flows through a wire.
Magnetic effect of current carrying conductor
Experiment: Make an electric circuit by putting a conducting
wire into hard paper. Keep the paper horizontal and spread some dust of iron on
the paper. Now connect the current through circuit or conductor and strike
slowly with your finger on hard paper.
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Magnetic effect of current carrying conductor
|
It is seen that the dust of the iron will get them arranged
like the figure above. If you draw a dot using a small compass and added to it,
you will find the same. If you change the direction of the current, the needle
of the compass will direct the opposite side which will remain facing to the
opposite direction. So the flow of electricity produced magnetic field around
the conductor also.
Solenoid
We can increase the magnetic field intensity by coiling the
above mentioned wire (see the figure below).
 |
| Solenoid |
Due to flow of the current through the coil, most of the
lines of the force will be concentrated in the center of the coil. The magnetic
field will be look alike the magnetic field of bar magnet. This type of coil is
called Solenoid. If we insert any iron rod through it, the iron rod will be
turned into magnet. If we stop the current, it will not remain magnet. If the
direction of current is changed, the pole of magnet will be changed. Through
this process, the iron is turned into magnet which is called electromagnet.
Electromagnet
If we insert any iron rod through the solenoid, we can get
more powerful magnetic field that the solenoid has. During the flow of current,
it is converted into more powerful magnet. This is called electromagnet. The
intensity of this magnet can be increased –
 |
| Electromagnet |
·
By increasing the flow of current.
·
By increasing the number of coil of the
solenoid.
·
By bending the iron rod in the form of alphabet
U and keeping two ends of U as close as possible.
Electromagnetic Induction
Many scientists tried to invent electric current from the
magnetic field when Oersted invented electromagnetic effect. Among the
scientists who worked on this subject, Michael Faraday of England, Joseph Henry
of America and H.F.E. Lenz of Russia achieved success individually. But at
first Michael Faraday published the result of his experiments in 1831.He shows
that a variable magnetic field can produce electromotive force which creates
electric current through a closed circuit. The phenomena to produce electric
current in a closed circuit by variable magnetic field are called
electromagnetic induction. Faraday made two experiments to invent
electromagnetic induction. You can also do the experiments.
 |
Electromagnetic Induction
|
Experiment: An
insulated wire is wound over a card board cylinder in the form of a coil.
Connect a galvanometer with two sides of this coil to understand the presence
of electric current. You have to open the non conducting cover during the time
of connection. Now insert the south pole of a magnet bar inside the coil.
What’s happening? Deflection of the galvanometer is taking place. It means the
current is flowing through the coil. Now remove the magnet. What’s happening?
The deflection of galvanometer will be the opposite of that time when magnet
was entered to the coil. If the magnet is kept stationary now, the galvanometer
will show the deflections when the coil is moved towards or away from the
magnet. If the coil is moved away from the magnet, we can see the deflection at
the opposite side.
Induced current and induced voltage
From this experiment, it is observed that the deflection of
the galvanometer proves the existence of an emf. So if we move a magnet towards
or away from the coil or if we move a coil towards or away from a magnet, the
electric current will be produced there. This is called electromagnetic
induction. If we move a coil towards or away from electric circuit or electric
wire, the electric current will be produced there also. This is also called
electromagnetic induction. So we can say that the process of creating electric
current through the change of the distance of the circuit which can create
voltage temporarily to another closed circuit is called electromagnetic
induction. This voltage is known as induced voltage and the current is known as
induced current. If there have no relative motion between magnet and coil, the
deflection will not be seen. The more will be the relative motion, the more
will be the deflection. So it is said that how long the relative motion will
last between magnet and coil, induced current will be durable for that period.
If the pole of magnet is altered, the side of induced current will be altered.
Induced current and induced voltage can be created in the following way:
·
By increasing the polar power of magnet.
·
By moving the magnet quickly.
·
By increasing the number of coil.
Effect of magnet on current carrying wire
We know that current carrying wire produced a magnetic field
of its own. There happens action and reaction between magnetic field existing
inside the opposite pole of a powerful magnet and the magnetic field of current
carrying wire.
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Effect of magnet on current carrying wire (Picture-1)
|
Put an electric wire between the two poles of a powerful magnet
like the picture. Let the electricity flow through this wire. You will see that
it will jump to the up. It is understood that a force is working on that. From
where does this come?
 |
Effect of magnet on current carrying wire (Picture-2)
|
If you look at the picture-2, you will see the lines of
force between the poles of the magnet. The magnetic field created by electric
current has also been shown.
 |
Effect of magnet on current carrying wire (Picture-3)
|
The lines of force created from the combination of two
fields have also been shown in the picture-3. The lines of force are more in
the down than that of the up of the wire. The reason is that both the fields
are working towards the same direction. [Again see the picture-2].The fields
above the wire are opposing each-other, some lines of force are rejecting
one-another. As a result the number of lines is less there. As the line wants to
keep them very tight to each other (like elastic rubber), they apply upward
force on the wire.
If the wire remains free, it moves upward. If the direction
of electric current is changed to opposite, the wire goes to downward.
Electric motor
Suppose a loop or coil of wire like picture-1 is used between the
two poles of magnet .As the loop has returned to the opposite direction from A
to B, the opposite electricity will flow between the two half of the loop or
coil. So, the wire will go to the upward in A and downward in B. For this the wire
moves in clockwise.
 |
Electric
motor (Picture-1)
|
At the vertical position of the wire like picture-2 no force will
act on it. For this it will be stopped. To keep the coil rotating, we will use
a device named commutator.
 |
Electric
motor (Picture-2)
|
It consists of two equal segments made of copper (see picture-3).
Each segment is connected to A and B respectively. The outer part of the
separated segment makes a contact with the electric source through carbon
brush. The segment moves with the coil and when its’ gap between two side
remains opposite to the carbon brush, no current will flow. But despite this
fact, the movement will remain continue for its inertia and it will get force
newly when it will come to the contact of the moving brush. Thus the rotation
will remain continue.
 |
Electric
motor (Picture-3)
|
It is noticeable that though A and B have changed their
position, the commutator current will enter from the right side of the loop
like before and will come out from the left, (see the picture-3) and the coil
will rotate clockwise. This is the principle of electric motor. Electric motor
converted the electric energy into mechanical
energy. To increase the speed and power of it, the intensity pf the
magnetic field will have to increase.
The intensity of the magnetic field can be increased in many
ways. These are:
·
By increasing the electric current.
·
By increasing the number of turn in the loop or
coil.
·
By using powerful magnet.
·
By increasing length and width of the coil.
The electric motor that we use also works in the same way. But
extra parts will have to add to increase the power and flexibility of the
rotation. Many coils or loops are made instead of only one coil or loop and
they are arranged neatly around the central axis or orbit. Each of these wires
is connected to its commutator. It helps to move continuously and easily.
 |
Electric
motor (Picture-4)
|
Each of coils is made of hundred scrape on the soft rod of iron
(which is called armature).For this, the armature is magnetized during current
flow and increase the intensity of the magnetic field. (In picture-4, two
broken lines of three armatures have been shown).The rotation can be increased
by picture-4 bending two sides of the magnet.
Uses: Electric motor is used to electric fan, pump, rolling mill
etc.
Generator
The electric machine in which mechanical
energy is converted into electrical energy is called generator. The basic
principles of this machine are established on the basis of electromagnetic
induction. Generator can be of two kinds. Such as
1.
AC generator
2.
DC generator
AC generator: The
structure and functions of it are being discussed in the following as it is
widely used:
 |
Generator
|
Structure: There is a field-magnet NS in it. There is
rectangular coil of wire in the middle of the magnet on the soft sheet of
iron (AB). The iron sheet is called armature. The armature is rotated at the
uniform speed in mechanical way on the middle of the magnet. The two sides of
the rectangular coil are connected to two slip rings.
The two slip rings can rotate to same orbit of armature. The two
carbon brushes are set in such a way that they touch the two slip rings when
the armature is being rotated. The resistance
R of external circuit is connected to the brushes.
Functions: When the armature undergoes rotation, the
armature coil intersects the lines of force of the magnetic field and
the electromotive force is induced in the coil according to electromagnetic
induction. As the two sides of the coil are connected to the external circuit a
alternating current is develop in the circuit. The magnitude of induced current
mainly depends on the intensity and speed of the rotation of the magnetic
field. During one complete rotation of the coil the direction of the induced
current is changed once. Thus the alternating current is produced from the mechanical
energy.
Transformer
The electrical device through which the high alternating
potential can be changed into low alternating potential and low potential into
high potential is called transformer. This device is made on the basis
electromagnetic induction. There are two kinds of transformers.
These are -
1. Step up
Transformer: The transformer which converts an electric current of greater
strength at a low voltage into an electric current of weaker value at high
voltage is known as step up transformer.
2. Step down
Transformer: The transformer which changes the high potential less electric
current into low potential much electric current is step down transformer.
End
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