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1. MAGNETIC EFFECT OF ELECTRIC CURRENT
FULL CHAPTER NOTES.
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2. What is a Magnet?
A magnet is defined as
An object which is capable of producing magnetic field and attracting unlike
poles and repelling like poles.
Properties of Magnet
Following are the basic properties of magnet:
•When a magnet is dipped in iron filings, we can observe that the iron filings cling to the
end of the magnet as the attraction is maximum at the ends of the magnet. These ends
are known as poles of the magnets.
•Magnetic poles always exist in pairs.
•Whenever a magnet is suspended freely in mid-air, it always points towards north-south
direction. Pole pointing towards geographic north is known as the North Pole and the
pole pointing towards geographic south is known as the South Pole.
•Like poles repel while unlike poles attract.
•The magnetic force between the two magnets is greater when the distance between
these magnets are lesser.

3. Bar magnet
A bar magnet is a rectangular object, composed of iron, steel or any form of a
ferromagnetic substance, that shows permanent magnetic properties. It has two
different poles, a north and a south pole such that when suspended freely, the
north pole aligns itself towards the geographic north pole of the Earth.

4. Magnetic field
The region around a magnet where its magnetic influence can be
experienced is called a magnetic field. The direction and strength of a
magnetic field are represented by magnetic lines of force.
Symbol B or H
Unit Tesla
Base Unit (Newton.Second)/Coulomb
A magnetic field is a vector field in the neighbourhood of a magnet, electric current, or changing electric field in which magnetic
forces are observable. A magnetic field is produced by moving electric charges and intrinsic magnetic moments of elementary
particles associated with a fundamental quantum property known as spin. Magnetic field and electric field are both interrelated
and are components of the electromagnetic force, one of the four fundamental forces of nature.

5. Magnetic field lines
•Magnet’s magnetic field lines result in the formation of continuous/running closed loops.
•The tangent to the field line at any given point indicates the direction of the total magnetic field at that
point.
•The greater the number of field lines crossing per unit area, the higher the intensity, the stronger the
magnitude of the magnetic field.
•There is no intersection between the magnetic field lines.
Magnetic field lines for a closed loop
Since magnets have dipoles, magnetic field lines must originate and end.
Therefore by convention, it starts at the north pole and moves towards the south
pole outside the bar magnet and from south → north inside the magnet. Hence, it
forms closed loops. The closer or denser the magnetic field lines, greater is the
magnetic field’s strength.

6. Iron filings test around a bar magnet
Iron filings around a bar magnet exhibit the magnetic field lines that engirdle
the bar magnet. The magnetic field lines can be explained as imaginary lines
that graphically represents the magnetic field that is acting around any
magnetic substance.
Magnetic field lines do not intersect as there will be two tangential magnetic
field directions associated with the same point, which does not occur. If a
compass needle is placed at that point, it will show two different directions of
the magnetic field which is absurd.

7. Magnetic Field Due to a Current Carrying Conductor
Oersted’s experiment
When electric current flows through a current carrying conductor, it
produces a magnetic field around it. This can be seen with the help
of a magnetic needle which shows deflection. The more the
current, the higher the deflection. If the direction of current is
reversed, the direction of deflection is also reversed.

8. Electromagnetism and electromagnet
An electromagnet is an artificial magnet which produces a magnetic
field on the passage of electric current through a conductor. This field
disappears when the current is turned off. The phenomenon of
producing or inducing a magnetic field due to the passage of electric
current is called electromagnetism.

9. Magnetic field due to a straight current carrying conductor
When current is passed through a straight current-carrying conductor, a magnetic field is produced
around it. Using the iron filings, we can observe that they align themselves in concentric circles
around the conductor.

10. Current is generally defined as the rate of flow of charge. We already know that
stationary charges produce an electric field proportional to the charge’s
magnitude. The same principle can be applied here. Moving charges produce
magnetic fields which are proportional to the current, and hence a current carrying
conductor produces a magnetic effect around it. This magnetic field is generally
attributed to the sub-atomic particles in the conductor, for e.g. the moving
electrons in the atomic orbitals.
A magnetic field has both magnitude and direction. Hence, it is a vector quantity
denoted by B (in the diagram below). The magnetic field due to a current-carrying
conductor depends on the conductor’s current and the distance from the point.
The direction of the magnetic field is perpendicular to the wire. If you wrap your
right hand’s fingers around the wire with your thumb pointing in the direction of the
current, then the direction in which the fingers would curl will give the direction of
the magnetic field. This will be clearer with the diagram below, where the red lines
represent the magnetic field lines.

11. Characteristics Of Magnetic Field Due To Current Carrying Conductor
The magnetic field produced due to a current-carrying conductor has the following
characteristics:
•It encircles the conductor.
•It lies in a plane perpendicular to the conductor.
•Reversal in the current flow direction reverses the field’s direction.
•Strength of the field is directly proportional to the magnitude of the current.
•Strength of the field at any point is inversely proportional to the distance of the
point from the wire.
•It’s difficult to comprehend the role of magnetism in our lives as we can’t see
them.
•Take a look around, and realising its importance will not be as difficult. The motors
that are used so extensively around the world, whether it’s toy cars or bullet trains
or aircraft or spaceships, all use the same magnetic effect.

12. Magnetic field due to current through a circular loop
The right-hand thumb rule can be used for a circular conducting wire as well as it
comprises of small straight segments. Every point on the wire carrying current
gives rise to a magnetic field that appears as straight lines at the centre.

13. Magnetic field due to current in a
solenoid
A solenoid is a coil of many circular windings wrapped in the shape of a
cylinder. When current is passed through it, it behaves similar to a bar
magnet, producing a very similar field pattern as that of a bar magnet. To
increase the strength a soft iron core is used.

14. Force on a Current Carrying Conductor in a
Magnetic Field
Ampere’s experiment
When an electric conductor is placed in a magnetic field, it experiences a
force. This force is directly proportional to the current and is also
perpendicular to its length and magnetic field.
Force on a straight current carrying conductor is mutually perpendicular to the
magnetic field and the direction of the current.

15. Magnetic Field In a Solenoid
A coil of wire which is designed to generate a strong magnetic field within the coil is
called a solenoid. Wrapping the same wire many times around a cylinder creates a strong
magnetic field when an electric current is passed through it. N denotes the number of
turns the solenoid has. More the number of loops, stronger is the magnetic field.
A solenoid is a type of electromagnet whose intention is to produce a controlled
magnetic field. If the purpose of a solenoid is to impede changes in the electric current, it
can be more specifically classified as an inductor.
The formula for the magnetic field of a solenoid is given by,
B = μoIN / L
Where,
N = number of turns in the solenoid
I = current in the coil
L = length of the coil.
Please note that the magnetic field in the coil is proportional to the applied current and
number of turns per unit length.

16. Fleming’s left-hand rule
Fleming’s left hand rule states that the direction of force applied to a current
carrying wire is perpendicular to both, the direction of current as well as the
magnetic field.

17. According to Faraday’s law of electromagnetic induction, when a conductor moves through
a magnetic field, an electric current is induced in it. Fleming’s right-hand rule is used to
determine the direction of the induced current.
When a current-carrying conductor is placed in an external magnetic field, the
conductor experiences a force perpendicular to both the field and the current flow’s
direction. Fleming’s left-hand rule is used to find the direction of the force acting on the
current carrying conductor placed in a magnetic field.

18. Electric motor
Electric Motor converts electrical energy into mechanical energy.
Current enters arm AB through brush X and current flows through brush Y from C to D. Using
Fleming’s LHR we find that the force pushes AB downwards and pushes CD upwards.
In an electric motor the split rings PQ act as a commutator that reverses the direction of the
current. The reversing of the current is repeated at each half rotation, giving rise to a
continuous rotation of the coil.

19. An electric motor is used to convert electrical energy into mechanical energy. Let’s go
through an instance: What does the mixer in your house do for you? The rotating blades
mash and mix things for you. And if someone were to ask you how that works, what would
you say? You would probably say that it works on electricity. Well, that’s not incorrect.
Motors convert electric energy to mechanical work. The opposite is done by generators that
convert mechanical work to electrical energy.
A simple motor has the following parts:
A power supply – mostly DC for a simple motor
Field Magnet – could be a permanent magnet or an electromagnet
An Armature or rotor
Commutator
Brushes
Axle

20. Power Source: A simple motor usually has a DC power source. It supplies power to the
motor armature or field coils.
Commutator: It is the rotating interface of the armature coil with a stationary circuit.
Field Magnet: The magnetic field helps to produce a torque on the rotating armature coil by
virtue of Fleming’s left-hand rule.
Armature Core: Holds the armature coil in place and provides mechanical support.
Armature Coil: It helps the motor to run.
Brushes: It is a device that conducts current between stationary wires and moving parts,
most commonly the rotating shaft.
Principle of An Electric Motor
The working of an electric motor is based on the fact that a current carrying conductor produces a
magnetic field around it. To better understand, imagine the following situation.
Take two bar magnets and keep the poles facing each other with a small space in between. Now, take a
small length of a conducting wire and make a loop. Keep this loop in between the space between the
magnets such that it is still within the sphere of influence of the magnets. Now for the last bit. Connect
the ends of the loop to battery terminals.
Once electricity flows through your simple circuit, you will notice that your loop “moves”. So why does
this happen? The magnetic field of the magnets interferes with that produced due to electric current
flowing in the conductor. Since the loop has become a magnet, one side of it will be attracted to the
north pole of the magnet and the other to the south pole. This causes the loop to rotate continuously.
This is the principle of working of electric motor.

21. Electromagnetic Induction and Electric Generators
Faraday’s experiment
•Faraday discovered that a magnetic field interacts with an electric circuit by inducing a
voltage known as EMF (electromotive force) by electromagnetic induction.
•Moving a magnet towards a coil sets up a current in the coil circuit, as indicated by deflection
in the galvanometer needle.

22. Electromagnetic induction
The phenomenon of electromagnetic induction is the production of induced EMF and
thereby current in a coil, due to the varying magnetic field with time. If a coil is placed near
a current-carrying conductor, the magnetic field changes due to a change in I or due to the
relative motion between the coil and conductor. The direction of the induced current is
given by Fleming’s right-hand rule.
Fleming’s right-hand rule
According to Fleming’s right-hand rule, the
thumb, forefinger and middle finger of the
right hand are stretched to be perpendicular
to each other as indicated below. If the
thumb indicates the direction of the
movement of conductor, fore-finger
indicating direction of the magnetic field,
then the middle finger indicates direction of
the induced current.

23. Electric generator
•The device that converts mechanical energy into electrical energy.
•Operates on the principle of electromagnetic induction.
•AC Generation: The axle attached to the two rings is rotated so that the arms AB and
CD move up and down respectively in the produced magnetic field. Thus, the induced
current flows through ABCD.
•After half rotation the direction of current in both arms changes. Again by applying
Fleming’s right hand rule, the induced currents are established in these arms along
directions DC and BA, therefore the induced I flows through DCBA.
•DC Generation: They work just like AC, instead use half rings to produce current in
one direction only without variations in magnitude.

24. What is an Electric Generator
Electric generators, also known as dynamos is an electric machine that converts
mechanical energy into electrical energy. The electric generator’s mechanical energy is
usually provided by steam turbines, gas turbines, and wind turbines. Electrical generators
provide nearly all the power that is required for electric power grids.
The reverse conversion of electrical energy to mechanical energy is done by an electric
motor. Both motors and generators have many similarities. But in this, the article let us focus
mainly on electric generators and how they convert mechanical energy to electrical energy.
Components of an Electric Generator
The main components of an electric generator are given below
The Frame – the structure
An Engine – the source of mechanical energy
The Alternator – produces an electrical output from the mechanical input
A Fuel System – to keep the generator operational
A Voltage Regulator – to regulate the voltage output
A Cooling System – to regulate heat levels that build up in the system
A Lubrication System – for durable and smooth operations over a span
An Exhaust System – to dispose of the waste exhaust gases produced in the process
A Charger – to keep the battery of the generator charged
Main Control – the control panel controlling generator interface

25. Domestic Electric Circuits
Fuse
•Fuse is a protective device in an electrical circuit in times of overloading.
•Overloading is caused when the neutral and live wire come in contact due to damage to the
insulation or a fault in the line.
•In times of overloading the current in circuit increases (short circuit) and becomes hazardous.
Joule’s heating (resistive or ohmic heating on the passage of current) in the fuse device melts
the circuit and breaks the flow of current in the circuit.

26. Domestic electric circuits
•Livewire has a voltage of 220 V and is covered with red insulation.
•Earth wire has a voltage of 0 V (same as Earth) and is covered with green insulation.
•The neutral wire has black insulation.
•In our houses, we receive AC electric power of 220 V with a frequency of 50 Hz.

27. Joule’s Law of Heating
Joule’s law is a mathematical description of the rate at which resistance in a
circuit converts electric energy into heat energy. The joule’s first law shows
the relationship between heat produced by flowing electric current
through a conductor
The amount of heat that is produced within an electric wire due to
the flow of current is expressed in the unit of Joules. When the
current flows through the wire there is a collision between
electrons and atoms of the wire which leads to the generation of
heat. Joule’s Law states that when a current flows in a conductor
the amount of heat generated is proportional to current, resistance,
and time in the current flowing. Let us have a look at the concept
behind the joule’s law.