Magnetic Field of Current || Class 10th Science || CBSE Notes || Study World
The term
Magnetic effect of Electric current was coined by Danish Physicist Hans
Christian Oerstedin 1820 who found that a current carring Conductor defects a
Compass needle due to production of magnetic field lines around it.
Importance of Magnetic Effect of Current :
The importance of magnetic effect of current
lies in the fact that it gives rise to some mechanical forces called magnetic field
lines due to which electric motor telephone lines works.
Oersted Experiment to demonstrate the magnetic
of Current :
Take a thin insulated copper wire such that
position A of it is in the North direction.
A Compass
needle is also near the wire. The two ends of the wire are Connected to a
battery through a key.
When no Current is following in the wire A-B
then the Compass needle remains parallel to the wire AB and point in the usual
north south direction as in figure
Now when the electric Current is passed through
the wire AB, then the Compass needle
will get deflect from original position.
When the direction of electric current is
reversed then Compass needle will get deflected in opposite direction.
Conclusion : This experiment explain that a current
carrying Conductor also posses magnetic field.
Magnetic field : The space surrounding a charged
bodies in which the force of attraction
or repulsion can be detected due to a magnet.
Magnetic
field lines: There are the lines in a
magnetic field along which north magnetic pole would move.
Characteristics of Magnetic field lines :
👉 They never intersect each other.
👉 They originate from north pole and end at South
pole.
👉 They are closer near the pole but are widely
Separated at &other place.
The magnetic Field lines Around a straight
Current carrying conductor arrange themselves in the form of Concentric Circles
whose centre lies on the Conductor.
Direction of magnetic field Line is by max well right hand grip
rule.
Maxwell's right hand thumb rule :Imagine you are grasping or holding the Current carrying
wire in your right hand. So that your thumb then the direction in which your
fingers encircle the wire will give the direction of magnetic field lines
around the wire.
Magnetic field pattern due to a circular loop of
wire:
Fix a circular wire of Circular loop fixed to a
thin Cardboard sheet. The two ends of the loop is connected to the two terminal
of the battery.
When iron filling are sprinkled over the Cardboard then they arranged themselves in a
form as shown in figure Near the coil the magnetic field lines are circular and
at the centre of the coil, they are parallel to each other also overlap giving
rise to a very strong magnetic field there.
Solenoid : It is a long circular coil of
insulated Copper wire having a large number of turns.
It is Used for making electromagnet
stronger magnetic field then a stronger current
carrying conductor.
Magnetic field pattern due to a current Carrying
Solenoid
Take a Solenoid SN whose two ends are Connected
to a battery through a key. When an electric Current is passed through the
solenoid In a magnetic field is produced in it whose pattern is similar to the
magnetic field produced by a bar magnet.
The magnetic field lines formed through the
solenoid at one end and return to another end as Shown in figure
Factors affecting the strength of magnetic field
produced by a current carrying solenoid :
The strength of magnetic field produced by a
current carrying Solenoid depends on :
(1) The number of turns in the solenoid :-Larger the number of turns in the solenoid greater
will be the magnetism produced.
(2) The strength of current in the solenoid : Larger the current passed through solenoid stronger
will be the magnetic field produced.
(3) The nature of core material used: The use of soft iron rod as core in a solenoid
produces the strongest magnetism.
(4) By reducing the radius of solenoid: We can also
increase the strength of solenoid
Electromagnet :
It is a temporary magnet which
retains its magnetic properties as long as the current passed through it. It Consists
of a solenoid bounded over a soft iron core and works on the magnetic effect of
Current
Uses of Electromagnet :- Following are the uses
of Electromagnet.
(1) It is Used in :
(a) Electric motor
(b) School bell (electric)
2) It is also used in lifting heavy loads in
industries
3) It is also used in separation of iron from
other substances.
4) It is also used in Scientific research
Factor affecting the strength of Electromagnet :
(1) The number turn in the Coil : If we increase the
number of turns in the coil the strength of electromagnet increases.
(2) The current flowing in the coil : If the current
in the coil is increased the strength of
the electromagnet increases.
(3) The length of the gap between its poles :-If we reduce the length of the air gap between the
poles of electromagnet then its strength increase. e.g. in case of u-shaped Electromagnet the strength
will increase.
Fleming left hand rule : To determine the direction of force acting
on current carrying Conductor placed in a magnetic field.
Hold the fore figure, centre figure, and -thumb
of left hand in Such a why that they mutually perpendicular to each other.
Now
adjust your hand such that the fore finger points in the direction of electric current
and then the direction in which your
thumb point will give you the direction of motion of the conductor.
Electric Motor :
It is a device which converts
the electrical energy into mechanical energy.
Principle
of Electric Motor :-It work on magnetic effect of current in which a Current
carrying coil placed in a magnetic field converts the electrical energy into
mechanical energy.
Construction of Electric Motor : It consists of a rectangular coil ABCD of
insulated copper wire bounded over a soft iron core and is called armature. The
armature is mounted over shaft to make things simple, it is not shown in
figure.
The coil s placed in between the two current
poles of a Strong horse Shoe magnet. So
that it can rotate freely between these poles.
The two end of the coil are then connected to
the two commutator half rings (Split rings ) of Copper XY which is also mounted
over the Shaft.
These rings prevents the twisting of the
connecting wires & reverse the direction of electric current in the coil
after every half rotation.
The half rings are then connected to the two
ends of the battery through two graphite brushes. P and Q which presses slightly
against the half rings through which the Current enters into the coll.
Working: Suppose the coil ABCD is in the
horizontal position and direction of magnetic field is from north to South
On pressing the Switch , the electric current
enters into the coil through PX flow in The direction DCBA and leaves via Y
& Q
Now by applying Fleming left hand rule to the
side DC & AB of the coil.
It is observed that the side AB is acted upon by
an upward force and CD by downward force.
These two equal and unlike parallel
force form a couple which rotate the coil in anticlockwise direction
As the coil reaches vertical position the carbon
brushes P & Q will touch the gap between XY to cut off the supply of
current to the coll. But due to the momentum gained by the coil it moves beyond
its vertical position, due to which Y comes in contact with P and X with Q und
the direction of Current gets reversed that is in the direction ABCD which
again rotate the coil. The above mentioned process repeat again and again and
the coil continuously convert electrical
energy into mechanical energy.
Fleming's Right Hand Rule for Direction of
Induced Current
Hold the thumb, the fore finger and the centre
finger of your right hand at right angle to one another as in figure.
Adjust
your hand in such a way that forefinger point in the direction of magnetic
field, and thumb points in the direction of the motion of conductor, then the
direction in which centre finger point gives the direction of induced current
in the conductor.
Direct Current and Alternating Current
If the current flows in one direction it is
Direct current. It is written in short
form as D.C. The current which we get
from battery is D.C
Whereas the Current which reverses its direction
after equal interval of time it is called as Alternating current. It is written
in short form as A.C. Most of the power station in India produced alternating
current.
Dynamo (Electric Generator).
DYNAMO : It is a device which convert the
mechanical energy of the steam, water and fuel into electrical energy.
Principle: Its working is based on the principle of Electromagnetic Induction.
Construction : It consist of rectangular coil
ABCD of insulated copper wire bounded over a soft iron core called armature.
The armature is mounted over the shaft.
The coil is placed in between the curve of a strong shoe magnet. So that, it can
rotate freely between the two Pole. The two ends of the coil are then connected
to commutator half ring of the copper x and y which are mounted over the shaft. These
half rings prevents the twisting of the
connecting wire. These half rings are connected to the two terminals of the battery.
Working: Suppose the coil ABCD is in the
horizontal position and move in anticlockwise direction. So the side CD is
acted upon by downward force and AB by upward force.
Now by applying Fleming right hand rule, it is
observed that the induced current is flowing in the armature coil in the direction
ABCD. After half rotation of the armature the arm CD moves upward and AB
downwards. Now induced current flow in reverse direction. The current flows in
the amateur along DCBA. Still the direction of the current in the external
circuit do not change after every half rotation. This type of generator is
known as DC generator.
Earth wire or Ground wire:- It is
the wire whose one end is Connected to the metal chasing of an electrical appliance and other to the ground by using a this pin
plug to avoid the risk of getting an electric shock.
Earth connection should be given to
those electrical appliances which draw heavy current, have metal surface such
as Cooler refrigerator, Electric iron, etc.
Safety fuse for Electric fuse :It is
a safety device consisting of short length wire made of this lead alloy having
high resistance and low melting point which melts and breaks the circuit when the
current exceed its safe value.
It works on the healing effect of
current and always put in a live wire in series to the appliances.
Important characteristics of Safety fuse :
(1) It should be a thin wire of high
resistance and low melting point. melting point.
(2) It should be usually made of tin,
tin- lead alloy or copper .
(3) The thickness of the fuse wire
should be such that it is able to melt when large current flow through it.
(3) Expensive electrical devices such as
TV, Ac, fridge should have their own fuse.
(4) It should be connected in series and
in the live wire.
(5) It should have proper rating.
Cause of a flow of amount of current
in domestic wiring:
(1) Short Circuiting: The touch of live and neutral wire directly is known as short circuiting.
When short circuiting occurs the
resistance of the circuit. So formed very very small & the current flowing
through the wire is very very large which heats up the wire to a dangerously
high temp & the fire may be stored.
(2) Over Loading: If too many electric appliances of high power rating such as gyser, heater, oven, toster, etc are switched on the same time. Then they drawn an extremely large current from the circuit due to which the household wire gets heated up to a dangerously high temperature and fire may be started.
(3) Hazards/ Dangers of Electricity : Though electricity is one of the
most important and convenient form of energy but its proper use is associated
with the following hazards or dangers:
(a) If a person happens to touch a live electric wire, he gets a serve electric shock or may even die.
(2) Short circuiting due to damaged wiring or overloading of the circuit can cause electrical fire in the buildings.
(3) The defects in the household wiring like loose connections and defective Switches Sockets and plugs can cause sparking and leads to fire.
Precautions in the Use of Electricity:
To avoid the hazards like electric Shocks or
electric fires. We should observe the following precautions in the use of
electricity.
(1) If a person accidentally touches a live electric
wire or if an electric fire starts in the house the main switch should be turn
off. At once , so as to cut off the electricity supply. This will prevent the
fire from spreading.
(2) All electrical appliances should be earthed.
(3) All the switches should be put in the live wire of the circuit.
(4) The fuse should always be connected in live wire in series and should be of proper rating.
(5) The household wiring should be done by using good quality by having proper thickness and insulation.
(6) While working on the live circuit for repair, rubber shoes and gloves should be used as they are insulators.
(7) The tools used for the electric repair should have proper insulation.
(8) One Should not touch the electrical appliances bare footed and with wet hands.
(9) Defective switches and loose connections should be removed immediately.
(10) All the wires should be covered withinsulating taps.
Difference between Electromagnet and Bar Magnet
Electromagnet
(1) It is a temporary magnet.
(2) It retain its magnetic properties as long as
current is passed through it
(3) Its
polarity can be changed by the direction of current.
(4) It strength can be changed.
(5) It can
produce very strong magnetic field.
Bar- magnet
(1) It is a permanent magnet.
(2) Its magnetic properties are permanent.
(3) Its polarity can't be changed.
(4) Its strength is fixed.
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