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Electromagnetism
Reversible demonstration alternator
Réf :
292 075
ENGLISH
In conclusion, when the winding direction of the turns in a coil facing a magnet
pole (north or south) changes, the voltage generated is inverted.
3. Theoretical alternator design
3.1 Statement of Lenz's law
The direction of the induced current is such that its effects oppose the cause
that created it.
3.2 Magnetic flux
Let N be the number of turns per row on the length L of the coil (L = 38 mm).
(The diameter of the copper wire that forms the coil is 0.2mm, while the
number of turns per row is N ≈ 190).
Let i be the number of the row of turns with radius r
i varies from 1 to n
(where n
T
The expression of the magnetic flux is Φ =
=
i
n
∑
T
π
2
N
r
If we let
= S
, be the sum of the areas of the turns making up the
T
i
=
i
1
coil, the expression for the flux becomes Φ = S
3.3 Arbitrary choice of the normal to the coil
The positive direction is chosen to be the turn winding direction. The right
hand rule gives the direction of the normal. (See diagram below)
3.4 Electromotive force (e.m.f) of induction : e
Any
variation
in
the
dΦ
=
−
e
expression
.
d
t
17
(for i = 1, r
i
≈ 33)
T
=
i
n
∑
T
π
2
N
r
i
=
i
1
r
B
.
T
flux
generates
an
+
r
n
e
Coil seen from the
bushings side
. = 4.5 mm)
i
r
r
B
.
n
.
r
n
.
e.m.f
given
by
the
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