Easy reference notes for ICSE and CBSE class X students

1. By
Excellence Classes
EXCELLENCE CLASSES

2. Content
 Orested’s Experiment
(Magnetic Field due to current carrying straight wire)
 Right Hand Thumb Rule
(Magnetic field due to current in a loop)
 Electromagnet
(Types & its uses)
 Comparison between Electromagnet & Permanent
magnet
 DC motor & its working principle
EXCELLENCE CLASSES

3.  Fleming’s Left Hand Rule
 Electromagnetic Induction
 Direction of Emf induced
1. Fleming’s Right Hand Rule
2. Lenz’s Law
 AC generator
 Advantage of AC over DC
EXCELLENCE CLASSES

4. Introduction
Hi dear students we are aware of Energy
conservation Act….according to which energy can be
converted from one form to another form. In this chapter
we will study how conversion takes place between Electric
energy and magnetic energy.
 For conversion of electric to magnetic field
(We will see Electromagnet concept)
 For conversion of magnetic to electric field
(We will see Electromagnetic Induction concept)
EXCELLENCE CLASSES

5. Orested’s Experiment
(Magnetic Field due to current carrying straight wire)
 Orested was the first to observe the relation between
electric and magnetic field.
 In his experiment, he used a wire which is carrying current
and a compass used for direction indication.
 The compass contains an needle made up of magnetic
material.
 He placed the compass directly over the wire.
EXCELLENCE CLASSES

6. Orested’s Experiment(continued.)
 Following are the results of the experiment:
1. When there is no current in the wire:-
Result:-
The compass needle points remains towards the north
EXCELLENCE CLASSES

7. Orested’s Experiment(continued.)
 Following are the results of the experiment:
2. When the current in the wire is in north direction
Result:-
The compass needle points towards the east.
EXCELLENCE CLASSES

8. Orested’s Experiment(continued.)
 Following are the results of the experiment:
3. When the current in the wire is in south direction
Result:-
The compass needle points towards the west.
EXCELLENCE CLASSES

9. Orested’s Experiment(continued.)
 Following are the results of the experiment:
4. If the compass is placed below the wire carrying the
current the results are reversed.
Snow Rule:- If electric current flows from South to North
direction in a wire kept over a magnetic compass, then the
north pole of the needle of a magnetic compass will be
deflected towards West.
Ampere's swimming rule:- It states that if a man swims
along the current-carrying wire, such that his face is always
towards the magnetic needle through which the current is
entering his feet and leaving from his head, then the north
pole of the magnetic needle is always deflected towards
EXCELLENCE CLASSES

10. Orested’s Experiment(continued.)
Conclusion:-
As the needle deflects east or
west only in the presence of the
current in the wire, Orested
concluded that “ the magnetic field
is produced around the current
carrying wire.”
EXCELLENCE CLASSES

11. Magnetic field lines due to current
in the straight wire
 Take a copper wire and connect it to the battery
supply with a key and pass it through the cardboard.
 Sprinkle some iron filling on the cardboard and switch
on the key so that the current will start flowing
through and wire.
 We will observe that the iron filling will arrange itself
to form concentric circles around the copper wire.
 Now if the direction of the current in the wire is
reversed by changing the polarity of the battery, then
also the iron filling forms concentric circles but in
opposite direction.
EXCELLENCE CLASSES

12. EXCELLENCE CLASSES

13. Magnetic field lines due to current
in the straight wire
 The concentric circles indicates that:-
1 As we move away from the wire, the distance
between the magnetic field lines increases
continuously.
2 That is, as we move away from the current
carrying wire, the magnetic field decreases
continuously.
EXCELLENCE CLASSES

14. Magnetic field lines due to
current in the straight wire
depends upon
1. As the current(I) in the wire is increased, the
magnitude of magnetic field(B) around the conductor
increases.
i.e B α I (B is directly proportional to I)
2. As we move away from the wire the magnitude of
magnetic field goes on decreasing.
i.e B α (1/ r) (B is inversly proportional to the radius)
Note:- B is magnetic field in Tesla
I is current in Ampere
r is radius of concentric circle in meter
B=k I/r
EXCELLENCE CLASSES

15. Right Hand Thumb Rule or Palm
Rule
 This rule is used to determine the direction of magnetic
field around a current carrying conductor.
 Statement:- If a current carrying conductor is imagined
to be held in right hand such that thumb points in
direction of current ,then curled fingers of hand indicate
the direction of magnetic field.
EXCELLENCE CLASSES

16. Magnetic field lines due to current carrying circular coil
•The magnetic field around straight wire
can be increased by bending the wire in
the circular coil.
•A circular coil is made up of large number
of very small straight wires.
•Sprinkle some iron filling on the
cardboard.
•The end terminals are connected to the
battery the current will start flowing which
will produce the magnetic field.
•Hence at the centre of the coil, the iron
filling will align almost in straight line and
perpendicular to the plane of the coil.
•At the two turns of coil, the iron filling will
arrange itself in an concentric circles.
•The direction of magnetic field produced
can be illustrated by Right hand thumb
rule
EXCELLENCE CLASSES

17. Magnetic field lines due to current carrying circular coil
depends upon
1 As the current(I) in the wire is increased, the magnitude of magnetic
field(B) around the conductor increases.
i.e B α I (B is directly proportional to I)
2 As we move away from the wire the magnitude of magnetic field goes on
decreasing.
i.e B α (1/ r) (B is inversly proportional to the radius)
3 As number of turns increases the magnitude of the magnetic field increases.
i.e B α n ((B is directly proportional to n)
Note:- B is magnetic field in Tesla
I is current in Ampere
r is radius of concentric circle in meter
n is number of turns
B=knI/r
EXCELLENCE CLASSES

18. Magnetic field lines due to current carrying circular solenoid
• Solenoid is a coil of many circular
turns of insulated copper wires
wrapped closely in the shape of
cylinder, such that the diameter of
coil is smaller than its length.
•When current is passed through
solenoid, each coil in it produce
magnetic field.
•As each coil carries current in same
direction, the magnetic field adds and
hence the resultant magnetic field is
large.
•The solenoid will act similar to
permanent magnet hence North and
South are produced at the ends.
EXCELLENCE CLASSES

19. Magnetic field lines due to current carrying circular solenoid
•The end of solenoid in which the current
flows in anticlockwise direction will act
as North pole
•The end of solenoid in which the current
flows in clockwise direction will act as
South pole.
•The material on which the solenoid is
wounded is called as core.
•The core may be air , iron , ferrite etc.
•Commonly the solenoid is wounded on
a non conducting hollow tube and the
iron core is inserted in it.
EXCELLENCE CLASSES

20. EXCELLENCE CLASSES

21. Magnetic field lines due to current carrying solenoid depends
upon
1 As the current(I) in the wire is increased, the magnitude of magnetic
field(B) around the conductor increases.
i.e B α I (B is directly proportional to I)
2 As we move away from the wire the magnitude of magnetic field goes on
decreasing.
i.e B α (1/ r) (B is inversly proportional to the radius)
3 As number of turns increases the magnitude of the magnetic field increases.
i.e B α n ((B is directly proportional to n)
4 Magnetic field depends upon the nature of core used (µ)
Note:- B is magnetic field in Tesla
I is current in Ampere
r is radius of concentric circle in meter
n is number of turns
µ is the permeability of core
B=µnI/r
EXCELLENCE CLASSES

22. Electromagnet
•An electromagnet is a coil of wire
wound on a soft iron core.
•It can act as an magnet only if
electric current is flowing through the
coil of wire.
•The use of iron core is to increase
the intensity of magnetic field.
•Depending upon the shape of the
iron core there are two types of
electromagnet:-
1. I shaped Electromagnet
2. U shaped Electromagnet
EXCELLENCE CLASSES

23. 1 I shaped or straight Electromagne
•An I shaped electromagnet is a coil of wire
of large number of turns wound on a soft iron
core.
•The two ends of the wires are connected to
the battery terminals
•An switch is connected to turn ON and OFF
the supply.
•As switch is turn ON the electromagnet will
act as magnet and North and South will
produced as per the thumb rule
•The use of iron core is to increase the
intensity of magnetic field.
EXCELLENCE CLASSES

24. electromagnet
•It is an soft iron core in U shaped
•Insulated copper wires are wound on the
both the limbs.
•The Copper wires A and B are wounds in
opposite direction on both the limbs such
that clockwise on one limb and anticlockwise
on other limb as shown in figure.
•Hence when switch is turned ON the current
will flow in opposite direction in coil A and B.
•Therefore one limb will act as North while
other limb will act as South pole.
EXCELLENCE CLASSES

25. Uses of Electromagnet
1. Electromagnets are used in many electrical
devices such as telephone , loudspeaker
electrical horn etc.
2. In industries to lift transfer iron, steel and
metallic scrap.
3. For seperation metals from non magnetic
materials
4. In Motor and Generators.
5. In hospitals, to attract a bit of small iron particles
entered in sensitive areas like eyes.
EXCELLENCE CLASSES

26. Comparision between Electromagnet & Permanent magnet
Sr.
No
.
Electromagnet Permanent Magnet
1
2 They are temporary magnets and can
produce magnetic field for the time when
current is flowing
They are permanent magnet unless they are
roughly handled or heated.
3 The magnetic field strength can be changed
by changing current or number of turns of the
coil.
The magnetic field strength cannot be
changed once made.
4 It polarity can be reversed Its polarity cannot be reversed
5 It has wide range of applications It has very limited applications
6 It can be easily demagnetised It cannot be easily de magnetised
EXCELLENCE CLASSES

27. DC Motor & its Construction
•The machine which convert electrical energy into mechanical energy is called as
motor
•The motor which works on DC supply is called as DC Motor
Construction:-
Following are the components of DC motor
1. Armature coil (Rotor) :- It consists of large
number of turns of rectangular coil made up of
copper and is wound over soft iron laminated
core.
2. Field Magnet (Stator) :-Pair of magnet
between which armature is rotating..It may be
permanent magnet or electromagnet.
3. Spilt Ring or Half ring :- Two ends of the coil
are welded to metallic rings connected to the
brushes
4. Brushes :- Made up of carbon and is stationary
which is in continues contact with rotor.
EXCELLENCE CLASSES

28. Working Principle of DC
Motor
When an current carrying conductor
(rotor) capable of moving freely between
magnetic field, it experiences force and starts
to rotate.
 The direction of rotation of DC Motor is given
by Fleming’s Left Hand Rule
EXCELLENCE CLASSES

29. Fleming’s Left Hand Rule
• It states that “ Stretch out the
forefinger, middle finger and thumb of
Left hand mutually perpendicular to
each other as shown in figure.
• If the forefinger gives the direction of
magnetic field, middle finger gives the
direction of current then the thumb
will denote the direction of force
acting on the rotor.
EXCELLENCE CLASSES

30. Fleming’s Left Hand Rule
N S
. x
Magnetic Field
f
o
r
c
e
f
o
r
c
e
Dot indicates outward current
Cross indicates upward current
I
In this case the motor is rotating in clockwise direction
EXCELLENCE CLASSES

31. Electromagnetic Induction
Introduction :
 Electricity has became the 4th most basic need
of human. Most of the devices contains electric
circuits in it.
 Hence Generation of electricity is most
important thing.
 Electricity can generated from wind energy,
thermal energy, nuclear energy, hydro energy etc.
 Generation of electrical energy from all the
above contains a common physics behind it that is
ELECTROMAGNETIC INDUCTION
EXCELLENCE CLASSES

32. Electromagnetic induction
 If magnetic field through an circuit changes, an
EMF is induced in that circuit.
 This Emf produced is called as induced emf and
the current is called as induced current.
 The induced Emf is Alternating in nature.
 The scientist Michael Farad and Joseph Henry
Conducted the experiment and stated the laws
regarding electromagnetic induction.
 Hence the law is called as Faraday’s Law of
Electromagnetic Induction
EXCELLENCE CLASSES

33. Experimental Setup For
Electromagnetic Induction
EXCELLENCE CLASSES

34. Experimental Setup For Electromagnetic
Induction
 An coil is wound on a soft iron core and it is connected across a
galvanometer.
 An galvanometer is an instrument which shows deflection when current
is passed through it.
 A bar magnet is moved as in following cases.
Fig A
The magnet is kept stationary. Hence no change in magnetic
field. No Emf will induced. So Galvanometer is show zero deflection.
Fig B
The magnet is moved towards the coil .Hence there is change in
magnetic field linking to coil. Emf is induced and Galvanometer will
show deflection at right side
Fig C
The magnet is moved away from the coil .Hence there is change
in magnetic field linking to coil. Emf is induced but with opposite
polarity and hence Galvanometer will show deflection at left side.
EXCELLENCE CLASSES

35. Hence EMF induced is Alternating in
nature
In India the supply frequency of AC supply is 50Hz
i.e 50 complete cycles are covered in 1 second.
EXCELLENCE CLASSES

36. Direction of Emf Induced is Given By
 Fleming’s Right Hand Rule.
 Lenz’s Law
EXCELLENCE CLASSES

37. Fleming’s Right Hand Rule
• It states that “ Stretch out the
forefinger, middle finger and
thumb of Right hand mutually
perpendicular to each other as
shown in figure.
• If the forefinger gives the
direction of magnetic field, thumb
gives the direction of motion of
conductor, then the middle finger
will denote the direction of emf or
current induced in the conductor
EXCELLENCE CLASSES

38. Lenz’s Law
 It states that the emf induced in the conductor, will
oppose the cause producing it.
 If the north pole of the bar magnet is brought near the
coil, the current in the coil will induced in such a way
that, front face will act as North pole. So current will flow
from in anticlockwise.
 If the north pole of the bar magnet is moved away from
the coil, the current in the coil will induced in such a way
that, front face will act as South pole. So current will
EXCELLENCE CLASSES

39. AC Generator or AC Dynamo
• The machine which convert mechanical energy into electrical energy
is called as generator
• The generators which generates AC supply is called as AC generator.
Construction:-
Following are the components of DC motor
1. Armature coil (Rotor) :- It consists of large
number of turns of rectangular coil made up of
copper and is wound over soft iron laminated
core.
2. Field Magnet (Stator) :-Pair of magnet
between which armature is rotating..It may be
permanent magnet or electromagnet.
3. Slip Ring or Half ring :- Two ends of the coil
are welded to metallic rings connected to the
brushes
4. Brushes :- Made up of carbon and is stationary
which is in continues contact with rotor.
EXCELLENCE CLASSES

40. EMF Induced in the AC Generator
Depends upon
 The number of turns of the armature coil.
 The magnetic field strength produced by field
magnets.
 The speed of rotation of rotor.
EXCELLENCE CLASSES

41. Compare DC Motor & AC
Generator
Sr No.
DC Motor AC Generator
1 The machine which convert
electrical energy into
mechanical energy is called
as motor
The machine which convert
mechanical energy into electrical
energy is called as generator
2 The motor which works on
DC supply is called as DC
Motor
The generators which generates AC
supply is called as AC generator
3 It uses spilt rings It uses slip rings
4 The motor speed can be varied. The generator speed is kept constant.
EXCELLENCE CLASSES

42. Advantage of AC over DC
 The AC supply voltage can be increased and
decreased by using transformer whereas DC
cannot.
 The AC supply can be easily converted in DC
supply.
 The AC voltage can be reduced by using choke coil.
 The AC supply generation is easy as compared to
DC generation.
 The AC machines are more robust than DC
EXCELLENCE CLASSES