Page 154 - Physics Form 5 KSSM_Neat

Figure 4.13 shows a direct current motor during the Brain-Teaser
first half of its rotation and the second half of its rotation.
An important component in a direct current motor is the Why is the commutator not a full
ring but a ring split into two halves?
commutator that rotates with the rectangular coil. The Can the commutator be split into
carbon brushes in contact with the commutator are in their more sections?
fixed positions.
KEMENTERIAN PENDIDIKAN MALAYSIA

First Half Rotation Second Half Rotation

Rotation Coil Rotation Coil
Permanent Permanent
C B
magnet magnet
B C

D A
S S

N A N D
Commutator Commutator
Carbon brush Carbon brush
Carbon brush Carbon brush
Y Y
X X
– + –
+
D.C. power supply D.C. power supply

First-half rotation Second-half rotation
Direction of current in the coil: ABCD Direction of current in the coil: DCBA

Carbon brush X in contact with red half of Carbon brush X in contact with blue half
the commutator of the commutator

Carbon brush Y in contact with blue half of Carbon brush Y in contact with red half
the commutator of the commutator

Direction of current in the coil Direction of current in the coil
A→B→C→D D→C→B→A

Side AB of the coil: force acts upwards
Side AB of the coil: force acts downwards
Side CD of the coil: force acts upwards Side CD of the coil: force acts downwards

Coil rotates in the same direction as the
Coil rotates in one direction first half rotation

Figure 4.13 Working principle of a direct current motor
144 LS 4.1.5