These notes are provide detailed information on the electrodynamics chapter in the Mind Action Series Physical Science Grade 12 textbook. These notes are colourful, have diagrams for further explanation and are very easily understood.
Chapter 8
{ Electric Motors }
o Use right
hand wire
rule
o Thumb =
direction
of current
o Curled
fingers =
mag field
direction
Coil @ horizontal eq ∴ force = @ a
maximum
Apply Flemings rule to one side only
AB moves down
CD moves up
∴ anti-clockwise
2 mag fields = present
Strong field pushes conductor into
the weak field
➢ Movement of conductor = motor
effect
Coil @ vertical eq ∴ force = @ a
minimum
(at top) direction = same [both to
right] ∴ strong
(at bottom) directions = opposite
[betw mag = to right but around
conductor = to left] ∴ weaken field
external circuit = highlighted
Fleming's Left Hand Brushes connect external circuit to
split ring commutator
Motor Rule ➢ Brushes = made of graphite
Finger @ 90 ° (allotrope of C) – non-metal that
to e/o conducts electricity
F = thumb (motion Split ring commutator function =
, Chapter 8
{ Electro-Magnetic { Generators / Dynamo }
Induction } o Converts mechanical energy
→ electrical energy
The principle of electro-
magnetic induction = if there is
a relative motion between a
conductor and a magnetic field,
an emf will be induced in the
conductor
Direction of mag field, direction
of motion of conductor &
induced EMF = @ right-angles Conductor = out mag field, ∴ x current
➢ In diagram, conductor = moved o When conductor in mag field &
upwards & current flows out of stationery ∴ = x current
plane of the page ➢ need Δ Φ for current to be
present
Move conductor in ∴ c = down
➢ Move conductors direction,
generator also changes current
direction
➢ ∴ prod alternating current
o Use Fleming’s RH gen rule to
Fleming's right Hand determine direction of current
generator Rule B
A
Coil || (horizontal) to field
o AB moves up
o Current flows from A → B
o After 180 °, AB moves down
Finger @ 90 ° to e/o o Current flows from B → A (∴
alternating current in coil)
F = thumb (direction of motion /
force)
B = 2nd finger, magnetic field
I = 3rd finger, direction of current
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