Chapter 5
Chapter 5
Chapter 5
Declined each
other
Flux Lines Characteristics
THE MAGNETISM TERMS AND DEFINITION
- The opposition to the production of flux in a material ,which corresponds to
resistance.
- The unit is Ampere turns / weber (AT/Wb)
- Formula,
• Permeability,µ
mmf Fm IN
S
- The permeability is the ability of a material to concentrate magnetic lines of flux.
The higher the permeability, more easily a magnetic field can be established.
- The absolute permeability o r for air, vacuum and other non magnetic material
r so
1, o
B
7
- Permeability of free space o 4 10 , ( H / m) for air H
PROBLEM
2:
Calculate the reluctance of an iron ring which has a length of 300mm, cross
sectional area of 150mm2 and relative permeability of the iron ring is 2000.
THE ELECTRICAL & MAGNETIC
QUANTITIES
• Comparison between electrical and magnetic quantities:
ELECTROMAGNETISM
Electromagnetism describes the relationship between
electricity and magnetism
• Figure (a) and (b) show that the two conductors A and B carry current in the same direction and in the
opposite direction, respectively.
• When they carry current in the same direction, the flux distribution is exhibited in Figure (a).
• The magnetic fields set up by the two conductors are in opposite direction. Hence, they attract each other.
• When they carry current in opposite direction, the flux distribution is shown in Figure (b).
• The magnetic fields are set up by two conductors are in same direction. Hence, they repel each other.
Conductor A Conductor B
Direction of current Direction of current
• Solution
NI 960 5
H 1500
l 320 10 2
B A 1.2 12 10 4 0.00144Wb
EXAMPLE 2
• A coil has 100 turns and current flow is 0.5A. If the magnetic circuit length is
10cm, find mmf and magnetic field force
Solution :
Fm IN 100 0.5 50TA
Fm 50
H 500TA / m
l 10 10 2
ELECTROMAGNETIC INDUCTION
• When a conductor is moved across a magnetic field, there is a relative motion
between the conductor and the magnetic field. Likewise, when a magnetic
field is moved past a stationary conductor, there is also relative motion. This
principle is known as electromagnetic induction and the resulting voltage is
an induced
Vindvoltage,
As the magnet moves slowly to the As the magnet moves more rapidly to
right, its magnetic field is changing the right, its magnetic field is changing
with respect to coil, and a voltage is more rapidly with respect to coil, and a
induced. greater voltage is induced.
• 2nd faraday law’s
- The amount of voltage induced in a coil is directly proportional to the number
of turns of wire in the coil (N).
-The Second finger represents the direction of the induced or generated Current (the
direction of the induced current will be the direction of conventional current; from positive to
negative).
QUESTIONS:
1. State and explain Faraday’s law of electromagnetic induction. What is Len’z
law?
2. State: (i) Fleming’s Right Hand Rule and
(ii) Fleming’s Left hand Rule
3. Calculate the relative permeability of an iron ring with reluctance of 350/ H,
length of 200mm, cross sectional area of 150mm2 (Assume: µ0 = 4π x 10-7 H/m)
(µr = 3031)