Data Sheet

-38-
45. Motor Speed
Build the circuit shown on the left and you will see the lamp (76) and the
star LED (70) are on while the motor (95) does not spin or spins slowly.
Because the motor (95) is in series with the star LED (70), and the star
LED (70) has a large voltage drop of about 3.5V, the voltage across the
motor (95) is small and thus it spins slowly.
46. Reversing a DC Motor
Build the circuit shown on the left, turn on switch (62) and you will see
the heart LED (69) and lamp (76) turn on, and the motor (95) spin
at the same time. Turn off the switch (62) and put the motor (95) in
backwards, reversing its direction (95 should be upside down now).
Press the switch (62) and the motor (95) now spins in the opposite
direction.
Notice that the direction the motor (95) spins is related to the direction
the current ows through the motor (95). This is because the force
created on the motor shaft is related to the direction that the current
ows through the magnetic eld in the motor (95). You can look up
Fleming’s left hand rule for more details on the relationship between the
current ow, magnetic eld, and force that creates motion.
WARNING: Moving parts. Do not
touch the motor during operation. Do
not lean over the motor.
!
WARNING: Moving parts. Do not
touch the motor during operation. Do
not lean over the motor.
!