Data Sheet
-47-
64. Electronic ‘AND’ Gate
Build the circuit shown on the left. Note that the lamp (76)
only turns on when both the switch (62) and press switch
(61) are ON.
In digital electronics there are seven logic gates: AND, OR,
XOR, NOT, NAND, NOR, and XNOR. This circuit represents
an AND gate. If ON = True and OFF = False then an AND gate
is best dened as: The output is TRUE only when both inputs
are True. Therefore, the two inputs represented by the press
switch (61) and the switch (62) must both be ON (TRUE) in
order for the output represented by the lamp (76) to be ON
(TRUE).
65. Internal Resistance of the Motor
Build the circuit shown on the left. Turn on the switch (62)
and you will see the lamp (76) light, the motor (95) spin, and
the heart LED (69) turn on dimly.
Motors that are spinning (in the ON state) have very low
internal resistance (less than that of the heart LED (69)).
Since the motor (95) in this circuit is in parallel with the
heart LED (69), the equivalent resistance of the parallel
combination is much lower than when only the heart LED
(69) is in the circuit.
Using Ohm’s law, you can show that this lower resistance
leads to lowering the voltage across the motor (95) and heart
LED (69), which is why the heart LED (69) is dim and the
motor (95) speed is lower. This also shows that when other
components are in series (like the lamp (76) in this project),
then placing components in parallel can have an effect on
each other.
WARNING: Moving parts. Do not
touch the motor during operation. Do
not lean over the motor.
!