Faraday’s Law
 If the flux linking a loop (or turn) varies as a
function of time, a voltage is induced between its
terminals.
 The value of the induced voltage is proportional to
the rate of change of flux.

EN
t
Where:
E = induced voltage [V]
N = number of turns in the coil
 = change of flux inside the coil [Wb]
t = time interval of the flux changes [s]
Lecture 02
Electro Mechanical System
1
Faraday’s Law
 Example:
A coil of 2000 turns surrounds a flux of 5 mWb produced. by
a permanent magnet.The magnet is suddenly withdrawn
causing the flux inside the coil to drop uniformly to 2 mWb in
1/10s. What is the induced voltage?
  (5m Wb  2m Wb)  3m Wb

EN
t
3  103
 2000
1 / 10
 60V
Lecture 02
Electro Mechanical System
2
Voltage Induced in a Conductor
 It is often easier to calculate the induced
voltage on a segment of conductor instead of
the voltage on a coil
E=Blv
Where:
E = induced voltage [V]
B = flux density [T]
l = active length of conductor in the
magnetic field [m]
v = relative speed of the conductor [m/s]
Lecture 02
Electro Mechanical System
3
Voltage Induced in a Conductor
 Example:
A stationary conductor of a large generator have an
active length of 2m and are cut by a field of 0.6 teslas,
moving at a speed of 100m/s. Calculate the voltage
induced in each conductor.
E = Bl v
E = 0.6 x 2 x 100
E = 120 V
Lecture 02
Electro Mechanical System
4
Lorentz Force on a Conductor
 A current-carrying conductor sees a force when placed in a
magnetic field
• Fundamental principle for the operation of motors.
• The magnitude of the force depends upon orientation of
the conductor with respect to the direction of the field.
• Force is greatest when the conductor is perpendicular to
the field.
 The Lorentz or electromagnetic force:
F = B l I Sin
Where:F = force acting on the conductor [N]
B = flux density [T]
l = active length of conductor in the magnetic field[m]
I = Current in the conductor [A]
 = Angle between the flow directions of current & flux
Lecture 02
Electro Mechanical System
5
Lorentz Force on a Conductor
 Example:
A conductor 3 m long is
carrying a current of 200 A and
is placed in a magnetic field
with a density of 0.5 T.
Calculate the force on the
conductor if it is perpendicular
to the lines of flux.
F = B l ISin
= 0.5  3  200  Sin 90
o
= 300 N
Lecture 02
Electro Mechanical System
6
Direction of Force on Conductor
 Current carrying conductor is
surrounded by a magnetic field.
 The flux lines of two magnetic
fields never cross each other.
 The flux lines of two magnet
fields are vectorally added.
 The generated mechanical
force tends to push the lines of
flux back to an even
distribution.
 Right hand rule
 Point fingers in the direction of
current flow (+ve to - ve).
 Bend fingers into the direction
of the magnetic field (N to S).
 Thumb points in the direction of
force .
Lecture 02
Electro Mechanical System
7