This document discusses magnetic circuits and concepts related to magnetism. It defines a magnet and explains that magnets have north and south poles where iron filings accumulate. It then describes the two laws of magnetism - like poles repel and unlike poles attract, and the force between poles is directly proportional to the product of their strengths and inversely proportional to the square of the distance between them. The document goes on to define magnetic field, magnetic lines of force, magnetic flux, pole strength, magnetic flux density, and how an electric current can produce magnetism in electromagnets. It concludes by explaining conventions for representing current direction and magnetic field direction graphically.

1. Magnetic Circuit
By,
Rohini Haridas
Assistant Professor,
Dept of Electrical Engineering,
SSGM College of Engineering,Shegaon

2. UNIT -II
Magnetism ElectromagnetismElectromagnetism
Electromagnetic
Induction

3. Magnet
• Magnet is an object
which possesses
property of attracting
iron and some other
metal pieces.metal pieces.

4. • When such a magnet is rolled
into iron pieces it will be
observed that :
• Maximum iron pieces
accumulate at the two ends of
the magnet
• while very few accumulate at
the centre of the magnet.
• The points at which iron pieces
accumulate maximum are
called poles.

5. When such a
magnet is
suspended freely
by the piece of silk
fibre, it turns and
always adjustsalways adjusts
itself in the
direction of North
and South.

7. Laws of Magnetism
Law 1 : It states that like magnetic poles repel and unlike
magnetic poles attract each other

8. Law 2 :
It states that, the force (F) exerted by one pole on other
pole is,
i. Directly proportional to the product of pole strengths
ii. Inversely proportional to the square of the distanceii. Inversely proportional to the square of the distance
between them
iii. Nature of medium surrounding the poles.
2
21
d
MM
F
∗
α

9. Magnetic Field
• The region around a magnet within which the
influence of the magnet can be experienced is
called magnetic field.
• Existence of such field can be experienced
with the help pieces of metals.

10. Magnetic Lines of Force
• The magnetic field of
magnet is represented by
imaginary lines around it
which are called magnetic
lines of force.lines of force.
• These lines have no
physical existence, these
are purely imaginary

11. Properties of lines of force
1. Magnetic lines of force start from the North Pole and
end at the South Pole
2. They are continues through the body of magnet
3. Magnetic lines of force always prefer a path offering3. Magnetic lines of force always prefer a path offering
least resistance.
4. Two magnetic lines of force can not intersect each
other.
5. They tend to contract in length

12. Magnetic Flux (φ)
• The total number of lines of force existing in a
particular magnetic field is called magnetic
flux.
• It is denoted by symbol (φ) and its unit is• It is denoted by symbol (φ) and its unit is
weber is denoted as Wb.
1 Wb = lines of force8
10

13. Pole Strength
• The capacity of pole to supply or accept
certain number of magnetic lines of force is
called as its pole strength.
• Unit of pole strength is weber as pole strength
is directly related to flux i.e. lines of force

14. Magnetic Flux Density (B)
• The flux per unit area (a) in a plane at right
angles to the flux is known as flux density.
B
φ
=
• Unit is or Tesla
a
B
φ
=
2
m
Wb

15. Magnetic Effect of Electric
Current(Electromagnets)
• When a coil or a conductor carries a current, it
produces the magnetic flux around it.
• Then it starts behaving as a magnet. Such a• Then it starts behaving as a magnet. Such a
current carrying coil or conductor is called an
electromagnet
• Flux produced can be controlled by controlling
the magnitude of current.

16. Cross & Dot Convention
Current INTO the plane of paper
Current Coming Out of the
plane of paper
*Current carrying conductor is represented by small circle

18. Right Hand Thumb Rule
(Magnetic field due to current carrying conductor )
Grip the current carrying conductor in the right hand, with the
thumb pointing in the direction of current, then the fingers
encircling the conductor point in the direction of magnetic field

22. Representation of direction of flux