Andres La Rosa
Portland State University
MAGNETIC INDUCTION
M. Faraday, J. Henry
Lecture Notes
PH-212
Lenz's Law
A practical way to figure out the
direction of the induced currents
B
Speed of the
magnet
v
Magnetic flux
A
N
S
Vector area
Magnet located far
away from the ring
Φm,1
R
Ring
The ring intercepts magnetic fields of
low magnitude
"The induced current will be directed so as to
oppose the change in the magnetic flux that
is taking place."
Induced
currentt
v
S
B
N
Magnet located
closer to the ring
Magnetic flux
Φm,2
Ring
The ring intercepts magnetic fields of
higher magnitude )higher than the
case shown above).
Comparison: Φm,2 > Φm,1
Magnetic flux
B
Change in the magnetic flux through a fixed ring
of area A.
Bmagnet
Notice, the magnetic flux through the ring increases
as the magnetic aproaches the fixed ring.
QUESTION: In which direction
should an induced current flow in
order to decrease the magnetic flux?
Binduced
a)
OR
Binduced
b)
We realize that the option b) should be the correct one.
Exercise. Indicate the direction of the induced
current in the ring
S
N
Z
Ring lies in the
XY plane
Alternative way to provide the answer about the direction
of the induced current:
S
N
.
x
Ring
Exercise. Indicate the direction of the induced
current in the ring
N
S
Z
Ring lies in the i
XY plane
i
Alternative way to provide the answer about the direction
of the induced current:
N
S
x
.
Ring
Faraday's Law
Electromotive force
Electromotive
force
Faraday's Law