slide on dc motor for topic electromagnetism f5

1. Turning Effect Of A Current
Carrying Coil In A Magnetic Field
• if a current carrying coil is placed in a magnetic field, a
pair of forces will be produced on the coil.
• this is due to the interaction of the magnetic field of the
permanent magnet and the magnetic filed of the current
carrying coil.

2. Catapult field of turning effect
• the direction of the force can be
determined by fleming's left hand rule.
• since the current in both sides of the coil
flow in opposite direction, the forces
produced are also in opposite direction.
• the 2 forces in opposite direction is called
a couple which produces a turning effect
to make the coil rotate.
• examples of electric equipment whose
operation is based on this turning effect
are
• the direct current motor
• the moving coil meter.
https://youtu.be/ORGlwSRRxkg

3. A couple is two equal forces which act in opposite directs on an object
but not through the same point so they produce a turning effect.
Turning effect of a couple
N s
F
F
Distance, s
The moment (or torque) of a couple is calculated by
multiplying the size of one of the force (F) by the
perpendicular distance between the two forces (s).
Moment of Couple = F x s
the higher the moment of a couple, the higher the turning effect (the conductor moves faster)

4. Calculating turning effect of a couple
N s
F
F
S = 5cm
N s
F
F
N s
F
F
S = 3cm
S = 0cm
𝜃 =90°
𝜃
𝜃 = 0°
When the 𝜃 between Force and
distance is 90°, couple will experience
the highest moment.it gives maximum
speed of rotation to the coil.
The moment is calculated:
Moment = F x 5 = 5F
As the coil rotates, the angle will
decrease, the perpendicular distance
also decrease causing the rotation to
slow down
The moment is calculated:
Moment = F x 3 = 3F
When the 𝜃 between Force and
distance is 0°, couple will experience
the 0 moment. Which means it gives
minimum rotation to the coil.
The moment is calculated:
Moment = F x 0 = 0F

5. • an electric motor converts electrical energy to
kinetic energy.
• it consist a rectangular coil of wire placed
between 2 permanent magnets.
• the coil are soldered to a copper split ring known
as commutator.
• 2 carbon brushes are held against the
commutator.
• the function of the brush is to conduct electricity
from the external circuit to the coil and allow the
commutator to rotate continuously.
• the function of the commutator is to change the
direction of the current in the coil and hence
change the direction of the couple (the 2 forces
in opposite direction) in every half revolution.
this is to make sure that the coil can rotate
continuously.
Direct current motor (DC motor)

6. Working principle of DC motor
https://youtu.be/JmGl3xFk3SM
STAGE 1 (ROTATION 0° - 90°)
• Coil is parallel to the
magnetic field.
• Current flow into coil
from S2 -> DC -> BA and
flow out through S1
• Coil experience maximum
speed of rotation
STAGE 2 (ROTATION 90° - 180°)
• Coil is perpendicular to
the magnetic field.
• Commutator is not
touching the brush.
• Coil moves because of
inertia
STAGE 3 (ROTATION 180° - 270°)
• Coil is parallel to the
magnetic field.
• Current flow into coil
from S1 -> AB -> CD and
flow out through S2
• Coil experience maximum
speed of rotation
STAGE 4 (ROTATION 270° - 360°)
• Coil is perpendicular to
the magnetic field.
• Commutator is not
touching the brush.
• Coil moves because of
inertia

9. Sine graph of a dc motor
0° 90° 180° 270° 360°/0°
Stage 1 Stage 2 Stage 3 Stage 4
Angle of
rotation
current
Position of coil in dc
motor

10. Application Of The Force On A Current Carrying Conductor In A Magnetic Field
YOUR TASK:
You are required to make an infographic poster on the working principle of device that is
applying the force of current carrying conductor in a magnetic field.
You may choose to explain on the working principle of:
- Loudspeaker
- Moving-coil meter
- Or any device that relevant
Your work must be submitted through Google classroom by 16/4/2020